Smalling has been pictured leaving a bar in the early hours of Saturday morning, where he was allegedly chanting club songs.
The 24-year-old was ruled out of the trip to West Ham with a hamstring injury, but showed no signs of the niggle affecting his mood.
Smalling had his arms outstretched and an eye-witness told the Manchester Evening News he was singing: "We'll do what we want. We'll do what we want. We're Man United. We'll do what we want."
Despite his injury, Smalling was also spotted running a short distance for his taxi.
"He'd obviously had a great night with his mates. They were singing football songs," the eye-witness told the Manchester Evening News.
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