The England international returned to action in the Red Devils' goalless draw against West Bromwich Albion after being sidelined with a leg injury for almost a month. The 31-year-old was left out of the squad against his former club and it had raised few questions amongst a section of United supporters.
The former Chelsea manager revealed that Rooney failed to make it to the training session and had pain in both ankles. Mourinho also informed that Antonio Valencia missed the Merseyside club's trip to United as the winger-turned-right-back was rested for the clash.
"Valencia is really, really tired. He come from Ecuador, arrive here, play 90 minutes, was a big effort for him, we need to protect him. Rooney yesterday had pain in both ankles, he couldn't train and he is not available," Mourinho explained, as quoted by the Manchester Evening News.
Ashley Young featured in the right-back position and moved to the other side of the back four in the second half, following the withdrawal of Daley Blind during the break. The former Aston Villa man was forced off the pitch with. Mourinho remains hopeful that Young's injury is not serious, who was replaced by Luke Shaw in the 65th minute against Everton.
"I am not sure yet [if it is a long term injury]. But Ashley is the player who did not play in many matches in the past couple of years. The start of the season he did not play a lot and now is playing match after a match. So hopefully it is fatigue and some pain," United manager told BT Sport.
Rooney and Young now join the long list of injured players at United. Mourinho is already without the services of centre-back pair of Chris Smalling and Phil Jones after the duo picked up "long-term" injuries while on international duty with England. In addition to this, Juan Mata is also recovering from a groin surgery which he underwent prior to the Red Devils' league clash against West Brom.