Zlatan Ibrahimovic and Paul Pogba will return to the Manchester United squad for the match against Newcastle on Saturday.
Striker Ibrahimovic has not played since suffering career-threatening cruciate knee ligament damage in April, since when he has left the club and rejoined. Star midfielder Pogba has been sidelined for two months with a hamstring problem.
On Ibrahimovic's earlier than expected return, Mourinho said: "He was as an injured player the same superb professional he is when he's fit, fantastic. He's a very important player for us.
"We were all saying in 2017 he would be back, but it is one thing on December 31, 2017 and another thing mid-November.
"Of course we welcome him back. He is an incredible personality, to fight such an important injury."
Pogba's return is no less significant given his imposing form at the start of the season and United's lack of a comparable understudy.
"I can say now because he's back, I don't like to speak while he's injured, you can clearly see there is a Manchester United this season before Paul's injury and after Paul's injury," said Mourinho.
"There are qualities in our football, qualities that influence our approach in matches, with Pogba and without Pogba. Simple as that."