The Swedish striker is joining on a free transfer from Paris St-Germain after running down his contract at the French champions.
Palmeri claims the 34-year-old has signed a one-year contract with the Red Devils and the club can extend for a further 12 months.
He tweeted: “Ibrahimovic has signed for Manchester United.
“Ibrahimovic has accepted the 1 year contract. No automatic options will trigger the 2nd. But Manchester United has option for 2nd year.
“Ibrahimovic wages should be approximately €17m (£13.3m).”