The striker is in contention to make his debut against Chelsea on Monday evening despite missing the club's trip to Marbella for a warm-weather training camp during the winter break.
Ighalo has instead been training in isolation to get up to speed, having not played competitively since early December.
But he arrived at Manchester United's Carrington complex on Sunday morning and trained with the squad for the first time ahead of the trip to Stamford Bridge.
“Yes, this weekend he [saw the] boys," Ole Gunnar Solskjaer told MUTV.
"Again, that’s going to be great for us, to not just add an extra body, but a personality, someone who can help and someone who scores goals.
"It gives the group a boost.”
Solskjaer kept his cards close this his chest when asked whether Ighalo will be involved at Chelsea, but suggested the striker won't need a lengthy settling in period.
The Manchester United bos added: “As a striker you don’t need too much time to get involved in a group because your chance is there on the training field or in a game," Solskjaer added.