Ibrahimovic had been expected to be sidelined until January after suffering knee ligament damage in April, but the 36-year-old Swede worked his way back to fitness two months ahead of schedule to make his comeback from the substitutes' bench in last Saturday's victory over Newcastle United.
His return could not have been timelier or more welcome for Mourinho. After rampaging through the first part of the season, when United netted 33 times in 11 games in all competitions, the goals dried up and only 11 have come in their past nine matches.
Much of the problem rests with the out-of-form Romelu Lukaku, whose 11 goals in those first 11 games have been followed by just one since.
As the Belgian struggled, United's other forwards failed to step up, with Marcus Rashford, Anthony Martial and Jesse Lingard contributing only two goals apiece in the past nine matches.
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Their low return has been one of the key reasons why United have fallen eight points adrift of Premier League leaders Manchester City ahead of Saturday's visit of Brighton and Hove Albion to Old Trafford.
Ibrahimovic, who scored 28 times before his injury last season, will not only bring goals back to Mourinho's forward line but competition for places, which could prove just as valuable.
Lukaku has been almost guaranteed a starting place this season, yet that will change when Ibrahimovic is back to full fitness and pushing for inclusion.
Mourinho is not yet sure how long that process will take but says he will resist the urge to rush Ibrahimovic.
"He is not ready," the former Chelsea, Inter Milan and Real Madrid manager admitted in a press conference on Friday. "Step by step, minute after minute, match after match.
"Normally he's going to have these periods of 15-20 minutes (as a substitute). One day we'll feel that he is physically ready."
Ibrahimovic will also bring an experienced, winning mindset to an unquestionably talented but largely youthful side.
"He's always here, he's always positive, he's a good influence," Mourinho added.
That influence will only increase once Ibrahimovic gets fitter and sharper.
Lukaku, Rashford, Martial and Lingard need to raise their game at the same rate or face losing their places to the lion.
(Reporting by Matt Westby, editing by Neil Robinson)
