Mourinho has claimed that he was "completely convinced" of the Red Devils captain featuring in the European match, but is wary of placing more pressure on the 30-year-old, whose performances continue to be closely monitored.
"I was completely convinced of playing him tomorrow," Mourinho told reporters.
"I'm not sure if I do that because with the situation that you create to him I think he really can't afford to have a performance that is not really good and I am here to protect him and have to analyse the best thing for him. If he is not totally ready for it, I will discuss that with the medical staff."
Rooney was dropped for Man United's Premier League clash with Leicester City last weekend, which the Red Devils won 4-1 in arguably their best performance of the season.