He made the shock move to the Red Devils on loan in the January transfer window, with the Nigeria international expected to provide attacking cover following the recent injury to Marcus Rashford.
Flores has had two spells in charge at Vicarage Road, and he worked with Ighalo in his first stint. Per Tom Dutton of the Evening Standard, the coach said some patience will be required following Ighalo's temporary switch from Shanghai Shenhua:
"Mainly, the problem is how they train in China. It is not the same as in England. Is he really ready for first-team matches in the Premier League because the physical difference is so big? He probably needs one month to recover the full rhythm.
"The good thing is he knows his body well, works hard on injury prevention, and he is always working after training. I should say, also, that I felt in China, he gave exactly the same effort and quality as he gave me four years ago. We had the feeling in China that he could recover a high level with any team in Europe."
On Tuesday, the Red Devils confirmed their new signing will wear the No. 25 jersey:
Ighalo spent two-and-a-half years at Watford. He was key to the side earning promotion from the Championship in his debut term, and he scored 15 goals in the 2015-16 Premier League season.
He was then sold to Changchun Yatai the following campaign. In three seasons in the Chinese Super League—two with Changchun and one with Shanghai—he has 46 goals.
Even so, it was a surprise to see United move for the 30-year-old on deadline day, given he has been playing outside European football's top five leagues for so long. B/R Football's Sam Tighe said he can see why the Red Devils snapped him up, though:
Football writer Sam Pilger noted that United have been able to add crucial depth:
It will be intriguing to see how quickly Red Devils boss Ole Gunnar Solskjaer thrusts Ighalo into action. After all, it's in the short term where he will be required, with Rashford's double-back stress fracture suffered in January set to leave him sidelined for a couple of months.