#1. United need to sign a center-back
The injury to French defender Eric Bailly, who has become one of the mainstays of the Manchester United defense, had also brought home the fact that United need another center-back. It's not a secret that United lack quality center-backs, who can stay fit for an entire season, and the likes of Phil Jones, Marcos Rojo, and Bailly are prone to injuries. Also, Axel Tuanzebe hasn't really proved himself at the Premier League level, although he had a brilliant season for Aston Villa last season.
Manchester United have been heavily linked with Tottenham Hotspur and England stalwart Harry Maguire and if they are able to get that deal sealed, thenUnited's defense will most likely have a better look about them. However, nothing is final about Maguire's arrival to Old Trafford yet, and if the deal fails to materialize and injuries crop up mid-season, then Solskjaer might see his team imploding once again.