According to Volker Struth, Jerome Boateng had the opportunity to leave Bayern Munich for Paris Saint-Germain back in 2019, but then-coach Niko Kovac blocked the move.
Kovac would not allow Boateng to leave because the replacement options that were presented to him were not acceptable. Boateng and Kovac, of course, went on to have a bit of rocky relationship.
Here is the account from Struth per Abendzeitung:
At the end of August 2019, FC Bayern and Paris St. Germain agreed that Jerome Boateng would move to the French capital for a €37 million transfer fee. But the switch never went through. Because: According to Struth, there was a condition of the then Bayern coach Niko Kovac: “He demanded a replacement for Boateng, as soon as it was found, Boateng was allowed to go. The Bundesliga season had already started, it was purely a precautionary measure by Kovac that he still wanted Boateng in the playing squad until a successor was signed.” Problem: “None of the replacement candidates had convinced Kovac. The coach had therefore vetoed the sale.”
Boateng ended up staying and being part of a dynamic sextuple-winning squad, so things worked out for everyone in the end.