Osimhen has been in excellent form for Napoli during the 2022-23 campaign, scoring 21 goals and registering four assists in 26 appearances in all competitions.
The 24-year-old's future is currently being called into question, with Man United believed to have identified him as a priority transfer target for the upcoming window.
Ighalo, who represented Man United on loan between January 2020 and January 2021, has urged his fellow Nigerian to make the move to Old Trafford if given the opportunity.
"I think it's a good fit because he is a young boy, he runs and he can score goals," Ighalo told Sky Sports News. "Having Victor Osimhen and [Marcus] Rashford in the top at Manchester United will cause any defender panic, because they are two fast players and they are goalscorers.
"I think he will fit in Manchester United so well. If he asked for my opinion and what should he do, I would advise him to join Man United because, for me, they are the biggest club.
"I know him so well, he's like a brother to me. We talk once in a while, I advise him, I talk to him and I tell him to keep working hard and believe in himself, which he is doing. He is on the right path.
"He is a goalscorer, he never stops. Osimhen is like an ant. He is a striker that doesn't give defenders a chance to rest; he is always going to be on you, he is always going to press you and he isn't afraid.
"He is somebody who has the heart of a lion. He will try and put his head on any ball to try and score, I know that. He takes risks and I think it would be a feat for Man United, just in the same way this Argentina defender [Lisandro Martinez] - The Butcher... you see that guy going for every ball. He is similar to Osimhen.
"We don't speak about what his future holds, that is the work of his agent and is his privacy, but if he asks me for my opinion and what he should do, I would say to join Manchester United because it is the biggest club."
Osimhen, who is also believed to be a target for Chelsea and Arsenal, recently talked-up a move to the Premier League amid the speculation surrounding his future.
The forward made the switch to Napoli from Lille in September 2020, and he has represented the Italian outfit on 88 occasions, scoring 49 goals and contributing 13 assists in the process.
Any move for Osimhen is likely to cost in excess of £100m, with the Blues in a strong position to negotiate a high price this summer, as his contract is due to run until June 2025.
Man United are also believed to be interested in Harry Kane, although they face an uphill struggle when it comes to convincing Tottenham Hotspur to sell to a domestic rival.