The Swede was left out of the matchday squad for Manchester United’s goalless draw against Southampton today.
Ibrahimovic, who has only just returned to the fold after spending eight months on the sidelines with a serious knee injury.
The 36-year-old had played against Burnley, but was replaced at half-time.
However, Mourinho has confirmed that Ibrahimovic is likely to spend more time on the sidelines.
Lukaku was stretchered off the pitch with an oxygen mask after a clash of heads in the first half with Wesley Hoedt.
Nine minutes off stoppage time was added on at the end of the half.
The draw against Saints ensured United will finish 2017 in third place in the Premier League.
Chelsea’s 5-0 win earlier in the day at home to Stoke saw them jump above United into second.