The former United fullback is currenlty a free agent and hoping to find himself a new club.
Fosu-Mensah told the Independent: “I’ll always be a fan of United.
“Always. I came there when I was 16, I left when I was 23. I’ve had many nice moments, won a couple of trophies, especially in my first season.
“We all know United, we all know the history of United, we all know what United stands for.
“Even this last season the Premier League was difficult for them but they reached the Europa League final, so it’s something in the DNA of the club that they always want to win trophies.
“I have analysed the manager (Ruben Amorim) and I have seen a little bit how he plays and what he wants from his players.
“Jeremiah St Juste from Sporting Lisbon is a good friend of mine and he had great words for the manager, so I’m positive that United brought in a good manager.”
I want Rashford to be happy
Fosu-Mensah also spoke of former teammate Marcus Rashford's situation at United.
"I just want him to be happy,” he added. “Everybody just wants him to be happy.
“The most important things is for him to feel good, for him to feel happy. Look, the quality is definitely there. Nobody needs to say anything about this quality, because he’s a top player.”