The former Watford striker sealed a last-gasp Deadline Day loan move to United from the Chinese Super League side Shanghai Shenhua after United failed with late attempts to sign Salomon Rondon and Josh King.
The 30-year-old arrived in Manchester on Sunday with United hoping he can provide a cutting edge after they failed to score in three successive Premier League matches for the first time since October 2016.
“This was an emergency signing,” the former United goalkeeper said on Sky Sports News.
“I can understand a lot of people taking about a scatter gun approach, well it had to be with Marcus Rashford being out.
“The top four is still possible for Manchester United, they had to go and get somebody.
“The boy that’s come in (Ighalo) has got nothing to lose, nobody expects anything unbelievable from him but they definitely needed somebody in that position.
“You never know. A long, long time ago Manchester United signed a certain Frenchman (Eric Cantona) who no one really expected much from and he ended up propelling them to one of their most successful seasons of all time.