Mourinho was pleased with Rashford's impact made in defeat to Manchester City.
Mourinho said: “I trust him completely. I know his future will be absolutely brilliant.
“He is mainly a No9 and if you want to play him in different positions, we need to work him, we need to improve him, but his big personality is there.
“People look to the football talent but the personality at this level is very, very important and he was showing that immediately.
“We can play him as a wide-man or we play with both strikers, which we can do perfectly like we did against Hull City.
"The kid gave us what we had needed in the first half. For me the next big game is against Feyenoord and the next game he is going to play."