Rooney was surprisingly omitted from Sir Alex Ferguson's squad at Everton on Saturday with the United boss claiming he did not want to subject his star striker to intense personal abuse.
Another theory is that Rooney was being punished for the allegations about his private life, although that would be a move Ferguson has not made before in his 26 years with the Red Devils.
Let me at them: Rooney (centre) was in fine spirits at training on Monday morning
It is understood that Rooney was surprised and disappointed to be told at Manchester's Lowry Hotel on Friday that he would not to be included.
However, Rooney seemed happy enough this morning, laughing and joking with his team-mates at the start of United's final training session prior to their meeting with the Scottish champions, Ferguson's old club.
And it would be a major shock if Rooney did not face Walter Smith's men as United look to make a positive start to their European campaign and erase the memory of Saturday's dismal draw at Everton when they concededtwice in stoppage time.
No laughing matter: Boss Ferguson looked more serious than Rooney in training
United were in command after Darren Fletcher, Nemanja Vidic and Dimitar Berbatov cancelled out Steven Pienaar's opener but Tim Cahill and Mikel Arteta stunned Ferguson's side at the death.
It seems Ferguson will be picking from strength as, with exception of Michael Carrick who is out for three weeks with an achilles injury, all Ferguson's 25-man squad were training.
That number includes Rio Ferdinand, who has yet to make an appearance this season but is fit again after suffering a knee ligament injury at the World Cup.
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