The Dutchman made just four Premier League appearances last season, but he refuted the idea that this was down to the Portuguese's preference not to use young players.
Fosu-Mensah pointed out that no player featured in more games for United last season than fellow teenager Marcus Rashford, with the England international racking up 53 appearances in all compeititons last time out.
"Marcus played the most games last season so I think what they say about him (Mourinho) is not true. He gives youth a chance," explained the Dutch youth international.
"I think as a young player you have to grab the chance with both hands."
Fosu-Mensah will be looking to make a bigger impact this season and if his comments are to be believed, he is working under the right manager to do so.