Chelsea manager, Thomas Tuchel has said Kevin De Bruyne needed to leave the club in 2014 in order to grow.
However, he insisted that Kai Havertz or Timo Werner will not need similar departures.
De Bruyne left Stamford Bridge in an £18million deal to Wolfsburg, before becoming one of the Premier League’s best playmakers at Manchester City.
The Belgian midfielder could win the title for the third time if City beat Chelsea on Saturday, with a Champions League final to come between the two English teams later in the month.
“I don’t know; I was not there. I can say that you can get caught up in the thoughts that it was a big mistake to let him go, but you never know.
“You don’t know what would have happened if he did not change the club back to Germany from Chelsea and then back to England after that.
“Maybe he needed it at the time. A different league, a different challenge to be at his best level.
“But what I can tell you is that this league here, because you draw a comparison to Timo and Kai’s situation. The league here makes you either do it or don’t do it,” Tuchel told reporters.