United returned to the league’s top four under the stewardship of Louis van Gaal last season, but finished 17 points behind winners Chelsea.
And Sheringham, who scored 47 goals during a four-year spell at Old Trafford, claims his former club would need to add at least five players to their squad over the summer, but warned it may not be enough to reclaim the Premier League trophy.
Speaking to Sky Sports News HQ, Stevenage manager Sheringham said: “It’s going to be really tough for Man United to win it. When clubs finish so far off the championship winners it’s very difficult in the next season.
“It’s kind of like stepping stones unless they go out and bring in five or six new players which would be a big transition for the club.
“They’ll have to be extra special to beat Chelsea or Manchester City next year, obviously that’s the aim. I don’t think it’s as easy as said than done.”
Sheringham, who was named manager at Broadhall Way in May, also expects United goalkeeper David de Gea to leave the club for a move to Real Madrid this summer.
According to Sky sources, Madrid are leading the chase to sign De Gea, who has one year remaining on his United contract.
When asked if he thought United would retain the Spaniard’s services for next season, Sheringham said: “Probably not when there has been so much speculation over the summer period.
“There’s even more talk about it and he only has a year left. I would presume that will go ahead for him at some stage to go to Real Madrid.”