Greater Manchester Police used a Twitter post to confirm news of the man’s arrest on suspicion of child neglect.
The force’s GMP Stretford account, which covers the Old Trafford area, said the Middlesbrough fan left his son while “he went into town celebrating their victory drinking” following Friday’s night’s win.
Around 9,500 away fans saw Boro knock United out of the FA Cup in a penalty shoot-out following a 1-1 draw after extra time.
“We have looked after the child with an unhappy mum on her way down from N/East to collect him.”
A police spokeswoman added: “In the early hours of Saturday 5 February 2022, police received a report of concern for the welfare of a child.
“Inquiries established that an 11-year-old boy was asleep alone in a hotel room in Trafford.
“A 35-year-old man has been arrested on suspicion of child neglect. He remains in police custody for questioning.”
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