On Wednesday, Mason Mount and Fikayo Tomori face the curious case of playing against the club that employs them.
Both are on loan at Championship-Derby County of Chelsea, who will meet in the fourth round of the Carabao Cup and, if selected, play at Stamford Bridge.
Borrowed players will not be able to deal with their home team in Premier League games – more of that later – but in English football league competitions, if granted, and Chelsea has done so.
Chelsea said the experience of "fighting the top-flight opponent" will benefit 19-year-old midfielder Mount, who was promoted to England at the beginning of the season, and defender Tomori, 20.
Derby boss Frank Lampard, Chelsea's top scorer so far, called it a "classic" move.
"I am very happy for these young Chelsea guys who have come through the system and dream of Stamford Bridge," said Lampard.
"I have to thank Chelsea very much because it was their call and their decision, and I think they have seen the bigger picture of what a great experience their players will have."
But will the decision come back to prosecuting the Premier League club? Here are seven lessons learned from past loan losses.
Loan sharks can strike early
Without doubt, Mount and Tomori will feel that they are proving against their home club, as Patrick Roberts did when he was loaned out of Manchester City to Celtic.
When the Scottish champions met City in the Champions League group stage in December 2016, Roberts needed four minutes to reach the Etihad Stadium for a smart solo.
City was already through and Celtic eliminated, but the winger had no qualms about celebrating his efforts in a 1-1 draw.
Will Mount and Tomori celebrate when they go online against Chelsea? Well, why not?
It can happen in Europe's biggest clubs
Fernando Morientes, who was five years and three Champions League winners in his career at Real Madrid, played in Bernabeu against Brazilian striker Ronaldo – the last new signing in the Galactico group in 2002.
In the 2003/04 season, he opted for a loan to the Ligue 1 in Monaco, which helped him to an unlikely place in the Champions League final and was with nine goals the best scorer of the competition.
Two of them arrived in the quarter-final against their home club.
Real was not shaken by Morientes' first lag, a late header in a 4-2 defeat at the Bernabeu. However, it proved crucial when Monaco staged a dramatic comeback in the Stade Louis II. with the total score 5-5.
The Spaniard put on Ludovic Giuly, who scored twice to give himself a lead as Monaco progressed and lost to Jose Mourinho's Porto in the final.
Learn from your mistakes
The Morientes saga may have led Real Madrid to limit the likelihood of a recurrence scenario, but fourteen years later they were almost bitten again.
Real agreed to pay Monaco £ 71 million for World Cup Golden Boot winner James Rodriguez in 2014, but after three stuttering seasons, the Colombian playmaker was loaned to FC Bayern Munich on a two-year loan.
Real probably drew the German giants in the Champions League semi-finals, with Rodriguez Joshua Kimmich built when Bayern slipped in the first leg, a 2-1 home defeat. In Bernabeu he scored another goal and scored the second goal of Bayern.
Rodriguez refused to celebrate his efforts and thanked the fans for the "ovations" he received in Madrid. Finally Bayern were beaten when Zinedine Zidanes Real secured a 2-2 draw for the final.
And talk about learning from mistakes …
Fool me once …
Wednesday's Carabao Cup victory will be neither the first nor the best-known case of a borrowed Chelsea player competing against his home club.
Goalkeeper Thibaut Courtois joined Chelsea in 2011, playing three games at Atletico Madrid and playing three games against the blues in Europe. He started with a 4-1 Supercup victory in 2012.
However, it was Courtois' role in the Champions League semi-final of the following season that sparked many discussions. This also meant that Uefa overruled an agreement under the loan agreement that would have resulted in Atletico Chelsea having to pay a reported fee of £ 5 million to participate in both areas.
Uefa said that any private contract between clubs that could influence player selection is "null, void and unenforceable." Courtois played and played well as the teams drew 0-0 in Madrid before Jose Mourinho's side won 3-1 at Stamford Bridge to reach the final.
Super submarines are a threat
Bayern München has achieved quite good results with long-term loans for some of the most important young talents in the world. Before Rodriguez there was Kingsley Coman.
The French winger was added to the Bundesliga in August 2015 by Juventus with a two-year loan from the Bundesliga and hit the Italians later this season in the Champions League.
Both stages ended after 90 minutes with 2: 2 – an extension. After Thiago Alcantara had shot the Bayern forward, the 19-year-old Coman put the game beyond his home club with a fourth goal.
So far, Mount has scored two goals in three Carabao Cup rounds and won penalties on penalties in the last penalty shoot-out.
The English youth international is a fitness doubt for Derby's trip to Stamford Bridge – maybe he's a threat instead?
The LuaLua rule
Many & ifs & # 39; here, but should Derby County be promoted and Mount and Tomori go on loan to Pride Park, then they could not compete in the Premier League against Chelsea.
The reason? Lomana LuaLua.
After failing to find the net for Newcastle throughout the season, the Congo winger was loaned to Harry Redknapps Portsmouth in February 2004. In Newcastle, however, no clause could be inserted, according to which LuaLua could not play against them.
Less than a month after his loan, he played in a 89th minute draw against Newcastle, whose coach Bobby Robson complained that "one of our players" had met against his team.
LuaLua celebrated a somersault on the square before pointing to the name on the back of his shirt and tearing it off.
He apologized to the Newcastle supporters, adding that he was glad to be "somewhere where someone wants me".
This resulted in a change in legislation in the FA and the Premier League, which means that loaners could not compete against their parent clubs in the league.
Do not ruin the national team of a country
At least for the Derby Lanees, South Korean Ahn Jung-hwan is unlikely to face a goal when he defeated Italy in the last 16 of the 2002 World Cup.
Ahn was loaned to the Serie A team by Perugia from the South Korean Busan Daewoo Royals, and when Italy's World Cup exit shot home, he was thrown as a rogue.
Perugia chairman Luciano Gaucci told the Italian newspaper La Gazzetta dello Sport: "This gentleman will never again regain a foothold in Perugia." He added that he "had no intention of paying a salary to someone who ruined Italian football."
Gaucci then went back bizarrely and tried to take the option to sign the striker permanently, but Ahn refused and said the club had "attacked my character".