Rashford came on at half-time of the Manchester derby as United fell to a 2-1 defeat to City on Saturday.
The 18-year-old is yet to start under Mourinho, but the Portuguese tactician is ready for that to change in the Europa League.
"For me the next big game is against Feyenoord and the next game he is going to play. That is the only thing I can say," Mourinho told UK newspapers.
