After a 5-0 thrashing at the hands of rivals Liverpool on Sunday, the Norwegian's position has come under further pressure, after the Red Devils previously arrested a slump with a Champions League win over Atalanta.
According to The Mirror, the Old Trafford hierarchy have now prepared a list of three possible managers to take over, should the current boss fail to reverse the side's fortunes.
The report suggests that the Red Devils have identified Zinedine Zidane, Antonio Conte and Leicester City manager Brendan Rodgers as their prime targets, with both Zidane and Conte currently out of work.
The duo left Real Madrid and Inter Milan respectively over the summer, with the Italian having guided the Milan giants to their first Serie A title in 11 years last season, after winning the trophy three times with Juventus and a Premier League with Chelsea, while Zidane boasts two La Liga titles and three Champions Leagues with Real Madrid.
Rodgers is said to remain a long-term target for Manchester United, having guided Leicester to consecutive fifth-placed finishes in the Premier League.