I have seen a speculation like this about Osimhen.
Source: Goal.comCould this really be true?

I mean is there really a chance that we can lose Osimhen in January? Because as far as I know he doesn't have a January clause and he is staying with Galatasaray until the end of the season.
I hope there isn't such option for him. Otherwise it would really be difficult to convince him to stay more than half a season. There will be an option to play in the Premier League on one hand in the end.
Until we get a report from Victor Osimhen, Manchester United, or Galatasaray, this news remains a rumor. The Nigerian international said one time that he is not considering leaving Turkey in January. He appreciates that Galatasaray gave him a lifeline when all hope was almost lost.
The temptation of moving to a big club like Manchester United will be strong but I hope he remains in Turkey and helps his current club with the League and Europa Cup. His transfer will also depend on the decision of Napoli.