Ibrahimovic, the club's top scorer last season with 28 goals, made a comeback in November from a long-term knee injury, but suffered a setback and has not featured since a 45-minute cameo against Burnley in the Premier League last December.
Mourinho expects the pair to return for the last-16 Champions League tie against Sevilla, with the first-leg in Spain on Feb. 21.
"They are working on the pitch but not yet with us as a group so they are not very close to a return," he told a news conference on Friday.
"I want to believe that by Champions League time, around the end of the month, they will be back."
Marouane Fellaini continues to struggle with a knee injury and the Portuguese manager confirmed the midfielder will remain on the sidelines for Saturday's league clash against Huddersfield Town.
The 30-year-old Belgian limped out only seven minutes after coming on as a second-half substitute in United's 2-0 league defeat at Tottenham Hotspur on Wednesday.
"It's not an ACL (anterior cruciate ligament), it's not a complete rupture of any structure of the knee, so we are not going as far as that. But we are probably going to lose him for a few weeks, but I cannot say how long at the moment," Mourinho said.
Heading into the weekend, Mourinho has conceded the title to runaway leaders Manchester City for the first time, adding United must now strive to be "first of the last" this season.
United are in second place, 15 points behind City with 13 matches left.
"The game is important because we need points to be the first of the last. We have to try to finish second," he said.
"We are better than last season in every aspect -- points, position, number of goals scored, conceded -- so we have to try to stay there."
(Reporting by Hardik Vyas in Bengaluru; Editing by Toby Davis)
