Stoke City manager Mark Hughes has questioned the mentality of some of the Manchester United players ahead of their Boxing Day clash.
United are in desperate need of a win, with Louis van Gaal's side on a run of six successive games without victory.
Their slump has seen them drop out of the top four and they now trail league leaders Leicester City by nine points.
Hughes, who won two league titles as a player with United in the early 90s, questioned the players' mentality under Van Gaal.
"I don't know what it's like there now," he said.
"But there was always an expectation we were going to win. We didn't hope to win, we expected to, no matter who we went up against.
"I don't know if that's their mentality at the moment. I suspect most of them have that. But if you're new to the club and you're trying to find your feet, and there's a period of transition for you as a player, then maybe some of them haven't quite got it."
Hughes added: "There have been many players who signed for Manchester United, and just couldn't deal with the expectation.
"It's a big demand. You want to go there, be successful and make an impact.
"Sometimes, if you don't do it initially, then it becomes more difficult the longer it goes on. It's not easy."