The former Paris Saint-Germain striker has played 73 minutes in five substitute appearances since returning from cruciate knee ligament damage against Newcastle in November.
There were fears that Ibrahimovic’s career may be finished after he suffered the injury during a Europa League quarter-final victory over Anderlecht in April.
The 36-year-old’s return to fitness came sooner than most expected, although it is clear that Mourinho is wary of asking him to do too much too soon.
United’s manager suggested a week ago that Ibrahimovic, who has yet to score since his comeback, is not yet ready to play a full 90 minutes, but the form of Romelu Lukaku may cause a rethink soon.
Lukaku did score the first-half winner on Wednesday as United beat Bournemouth, 1-0, at Old Trafford, but has looked below par for the past two months, with just three goals in 15 games.
“There will be a bit of rotation,” said Mourinho without directly addressing the Lukaku situation.
“I’ll change a few players from match to match, because I think it is almost impossible for players to play all these matches in December and the beginning of January.”
– ‘Pressure to win games’ –
Lukaku’s goal did at least lift the mood at United, which was pretty low after last Sunday’s home defeat by neighbours Manchester City.
Manchester United striker Romelu Lukaku has looked below par for the past two months, with just three goals in 15 games
It was a result that left Mourinho’s side still second in the league but now 11 points behind Pep Guardiola’s leaders and with diminishing hopes of getting back into the title race.
Mourinho tried to put the 38 points his side have accrued into some perspective.
“We are second. The number of points could be first in other seasons, but we are second,” said Mourinho.
“We go one match at a time and let’s see at the end of the season how many points we have and where we are.”
A further setback off the pitch came with Mourinho’s confirmation that centre-back Eric Bailly, who has not played since November 5, needs ankle surgery and is likely to be out for the next three months.
Sunday’s visit to The Hawthorns may not necessarily offer an easy way to lift the mood.
Albion are on a club-record run of 16 matches without a victory, and have not scored in three games since Alan Pardew took charge, but they drew 0-0 at Liverpool on Wednesday with a disciplined display.
Prior to that they dropped five points against fellow strugglers in a 0-0 home draw against Crystal Palace and a 1-0 defeat at Swansea.
“They (the fans) understand the opposition is different this time (to Crystal Palace), they’ll probably give us a bit more licence,” said Pardew.
“That’s natural when you come up against top opposition, our players should gain confidence that there’s no massive pressure on them.
“There is a pressure in terms of where we are in the league. It’s a pressure to win games.”
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