Former Manchester United captain Gary Neville has suggested that the club need to sign a new centre-back in this window.
The club has been linked with moves for the likes of Sergio Ramos and Nicolas Otamendi, but so far midfielder Daley Blind has partnered Chris Smalling in defence.
Neville told Sky Sports News: "Everyone thought they were going to sign a Ramos or an Otamendi - those types of players - and that a big player would have been signed in the centre-back position.
"I don't think anyone would have foreseen Daley Blind playing centre-back. I gave him man-of-the-match on Friday night [against Aston Villa] but I think it's more of a stop-gap rather than a long-term solution. He knows what Van Gaal wants."
Blind has played in a variety of positions since he signed last season, including central midfield and left-back.