The Nigeria international signed for the club he supported as a boy on transfer deadline day on loan from Chinese Super League side Shanghai Greenland Shenhua.
While the move came out of nowhere and was a surprise to many, the striker does have pedigree in the Premier League from his time with Watford.
The 30-year-old bagged 15 goals in 37 top flight games for the Hornets in the 2015/16 season alongside current captain Troy Deeney.
Deeney insists he is delighted to see his former teammate get the move to the team he supports and claims the hitman was desperate to score against them for Watford.
"He's a good friend of mine, Odion," Deeney told Sky Sports . "I've got a lot of respect for him as well. When people get to know his back story, they will see a more human side to him. He's a talented footballer too.
"He's got his childhood dream to go play for his childhood club, so you have to tip your hat to him.
"When we played Manchester United [in 2015/16] he built up this thing where he felt he had to score, especially after scoring against Liverpool before that.
"He had about 19 shots in that game. He was desperate to score against United. He probably should have passed to me for one of them, and we could have won!
"I told him to calm down before the game, I wasn't so nice after the game! We laugh about it ever since. I wish him all the best."
Ole Gunnar Solskjaer was desperate to brining in attacking reinforcements in January after Marcus Rashford was ruled out for several weeks.
The club were linked with the likes of Edinson Cavani and Moussa Dembele, while Bournemouth striker Josh King was also mentioned.
In the end though they had to settle for the loan acquisition of Ighalo, certainly a gamble with a place in the top four up for grabs.
Ighalo has scored 16 goals in 35 games for Nigeria and will be hoping to prove his worth in front of the Old Trafford faithful when he gets his chance.
He could make his debut for the Red Devils when they travel to Stamford Bridge to face Chelsea on February 17.