Osimhen has joined Fener's great rivals Galatasaray on-loan from Napoli.
Mourinho said of the Nigeria striker: "Osimhen is a fantastic player. If I were in a club that can spend 70-75 million euros, I would buy him.
"I have no problem with Victor, I have a good relationship with him, even if he goes down a lot. I told Osimhen: 'Look, you are one of the best players in Africa together with Salah. Before there were Drogba, Eto'o, Weah. You can't fall down that much!'"
Of his own ambitions, Mourinho continued: "I think that on Thursday we will train with the full team for the first time. The growth of the players is quite good; of course, 12 points in 4 games would have been perfect, but we have to accept reality.
"In the Champions League we should have gone through, we have to accept this too.
"First of all I want to move forward in the Europa League. It's a new format and unknown to everyone, but we have to try. I've coached 200 matches in Europe, but this time it will be different.
"The referees? I've never had any problems with UEFA. I have a great relationship with the president, I'm part of their history and they know it. In the Europa League final against Sevilla, the VAR and the referee decided that we shouldn't have won the match, while for 1 million people it was a penalty.
"This year against Lille a very strange penalty was awarded."