The better Jadon Sancho does at Borussia Dortmund, the more questions asked of Manchester City's decision to allow him to leave in 2017.
In reality, City couldn't offer Sancho the first team football he desired, and at the time Sancho was not the player he has become. City, Sancho and Dortmund can all claim to have done well out of the £8m transfer in hindsight.
Sancho could command over £100m if he leaves Dortmund this year, though, so however much City may have been right to negotiate a transfer for their talented winger back in 2017, they will be reluctant to see many more repeats of players developing into world class talents away from the Etihad and earning another club money that could have been kept at the CFA.
So which other former City youngsters could come back to haunt the club after leaving in search of first team football?
Douglas Luiz
City didn't want to lose Luiz last summer to Aston Villa, but work permit issues meant they had no choice but to sell for £15m. The Brazilian has taken to life in the Premier League well and shown City that he could have added value in defensive midfield to relieve pressure on Fernandinho last season and Rodri this year.
He could still return to City, but his form at Villa Park will undoubtedly have alerted other clubs to his talents. He won't want to come back to play second-choice.
Rabbi Matondo
Matondo's exit last season to Schalke was a similar one to Sancho's - a talented young winger too good for the U23s but not ready to push Raheem Sterling and Leroy Sane out of the first team.
The Wales international, 19, took a while to get used to life in Germany before scoring on his first appearance of the 2019/20 season. However, that remains his only goal in 21 appearances. Just like Sancho, Matondo could attract attention if he gets on a run in Germany.
Jeremie Frimpong
Energetic right-back Frimpong left the CFA last summer and has started well at Celtic. His two goals and four assists from 22 appearances is a good return from defence, and he already has a Scottish League Cup win to his name.
Plenty of players have made the successful switch from Celtic Park to the Premier League, and Frimpong's experience at a huge club like Celtic won't do him any harm if he has ambitions of making it in England.
Javairo Dilrosun
Winger Dilrosun, 21, left City in 2018 and went largely under the radar, but got off to a flying start at Hertha Berlin with two goals and three assists in his first four league appearances.
There was talk Dilrosun could take a similar path to Sancho over at Dortmund, but a four month absence one year ago halted his progress. Another run of three goals and two assists from four games at the start of this season showed his potential again, but he has struggled for consistency since.
There's clearly a talented player there, and Dilrosun has shown flashes of the form that has taken Sancho from City's U23s to a world-class winger.
Taylor Richards
Richards was one of City's more highly rated forwards at youth level last season, but left in the summer and joined Brighton. He has continued his fine form for their U23 side, including a respectable goal and assist from four EFL Trophy games against league opposition this season.