The Nigeria international has been in excellent form for the newly-promoted side over the first half of the season, helping the Hornets to ninth in the standings.
Ighalo has netted 14 goals in 20 appearances this season and has been linked with a move to Spain, but insists he would like to stay in the Premier League.
“There has been speculation from Spain and Italy but I’ve played there and now want to play in England,” he said.
“I don’t think I will be moving but I’m not sure I’d say no if United called.
“They were my team growing up. I loved watching Andy Cole and Dwight Yorke on TV.
“They were my idols and playing at Old Trafford has always been a dream.”