Ibrahimovic sat out Tuesday's first leg of the EFL Cup semi-final against Hull City at Old Trafford, where second-half goals from Juan Mata and Marouane Fellaini secured a 2-0 win for United.
Veteran striker Ibrahimovic, who has 18 goals in 28 games across all competitions this season, was laid low through illness, although Mourinho does not foresee this being an issue when he attempts to take a chunk out of the five-point gap between Jurgen Klopp's second-place side and his own men in sixth on Sunday.
"Zlatan is ill, so no problem I think he will be fine," Mourinho told a post-match news conference, before explaining defender Marcos Rojo is a doubt for the weekend due to a muscular problem.
In Ibrahimovic's absence, it was left to another imposing penalty box presence to seal victory over a heavily depleted Hull.
Fellaini has rarely been anything approaching a fans' favourite at Old Trafford - a status Ibrahimovic claimed almost instantly after joining from Paris Saint-Germain last year - and the Belgium international's standing took another hit when he gave away a penalty to hand Everton a 1-1 draw against United at the start of December.
After he rose to nod Matteo Darmian's cross past Eldin Jakupovic in the Hull goal, Fellaini raced towards the dugout to embrace his manager, who in turn praised his mental strength.
Asked whether he had helped Fellaini over recent weeks, Mourinho said: "Yes, but that's the reason I am here. He is very strong in mentality and he coped well in the situation.
"He was not afraid the next match after Everton to come to the game again.
"He was phenomenal against Reading [last Saturday's 4-0 FA Cup win]. He knows that he is a very important player for me."
FEATURED IMAGE CAPTION: Manchester United striker Zlatan Ibrahimovic.