England star Smalling, who is recovering from a hamstring injury, was pictured chanting United songs in Manchester in the early hours of Saturday.
Smalling, 24, and a group of friends were seen singing: "We're Man United - we'll do what we want" at around 3am after leaving a bar in the city centre.
Moyes took a dim view of the episode and has warned the Reds' £50,000-a-week defender about his future conduct, although it is not yet clear if he has been fined.
United boss Moyes confirmed he had spoken to Smalling and said: "I've dealt with it and I've spoken to Chris. That would be as much as I would want to say on it."
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