Former Manchester United striker Lou Macari believes Louis van Gaal may sign a defender before the start of the season.
The Premier League giants have returned to England following their pre-season tour of the United States. They registered three victories over Club America, San Jose Earthquakes and Barcelona, while suffering a 2-0 defeat to Paris Saint-Germain in the last match.
United will host Tottenham Hotspur in the opening match of the season at Old Trafford on 8 August. Van Gaal has already confirmed summer signing Matteo Darmian, Daley Blind and Luke Shaw will start in the back four.
Macari says the PSG defeat shows vulnerability in United's defence and he also criticised his former club's display against the Ligue 1 winners.
"I still don't think they know their best partnership at the back – maybe someone will come in before the start of the season," Macari told talkSPORT.
"Last night [defeat to PSG] was a bit of a shock to everyone in the camp. Everyone was thinking the team was in a great shape but against PSG they let themselves down defensively – they were poor."
The Red Devils were after Real Madrid defender Sergio Ramos as the former Barcelona and Bayern Munich manager had identified him as a summer target for United. However, The Daily Mail reports the Spain international is set to commit his future to Real by signing a new five-year deal.
The Mirror claims United have turned their attention to signing Everton centre-back John Stones. They are willing to include Jonny Evans as part of the deal in order to beat Chelsea for the defender's signature.
United have already signed Memphis Depay, Bastian Schweinsteiger, Morgan Schneiderlin, Matteo Darmian and Sergio Romero this summer. Macari says the existing squad is good enough to challenge Chelsea for the title in 2015/16 season.
"I'd expect them to be title contenders - they're Manchester United and they've improved the team," the former United striker added.
"Last season United were poor, I don't think they'll make the same mistakes as they did at the start of the last campaign – if they have a horrendous first month then alarm bells will be ringing, but I expect them to do well."