David Moyes has stated that some of the criticism aimed at his Manchester United players by the former captain Roy Keane and goalkeeper Peter Schmeichel is correct. The manager also has an ever-deepening injury crisis with the "blow" of Robin van Persie being out for a month with a thigh injury which means United are without six key players, though Moyes denied the Dutchman was rushed back early following a groin problem.

The Scot takes the side to Aston Villa on Sunday, with United having lost their past two league games, to Everton and Newcastle United. They were also unconvincing in Tuesday evening's 1-0 win over Shakhtar Donetsk in the Champions League.

Keane criticised the team at half-time of the Donetsk match for failing to close down space and failing to make tackles, singling out Rio Ferdinand and Ashley Young as individuals whose general play was poor for special mentions.

Schmeichel claimed that Moyes needs to sell "five or six" players. Asked specifically about this comment, who is a club ambassador, the manager said: "The players would be the first to accept that we need to play better and we have to make that happen. I take responsibility. I need to make them play better because I'm the manager and I'll do that.

"Some of what they're [Keane and Schmeichel] saying is correct. There's some of it that's not correct because it's certainly not the [United players'] attitude or effort because they're really trying. I can only tell you every time we've played a game we haven't won, the players have been distraught by it and there's been a real toughness in them to try to put it right."

Moyes also denied Keane's claim that Sir Alex Ferguson still wields power at the club, saying that rather than his predecessor interfering, it is the 49-year-old who asks him for advice. "100%, yeah," said Moyes. "I can pick up the phone to him when I need to, which I do now and again. Obviously we bump into each other because he's a director; we say hello after the games. He doesn't [come to the dressing room]. A lot of the directors do but Alex keeps away from it."

Van Persie suffered his injury while taking a corner during the Shakhtar match. The thigh strain follows niggling groin and toe problems that have disrupted his season. Van Persie's career at his previous club, Arsenal, was injury-blighted before he recovered to be consistently fit in his final campaign. He was also able to play regularly for United last season and Moyes has no concerns about the striker's long-term availability.

"Robin has been great. I know a lot of people have said things [about him being unhappy] but Robin has been fantastic. He has been great to work with, we've looked after him, we've tried to train him and do it the way he needs to work. We've made sure he does that and I'm sure he'd be the first to accept that."

A groin injury ruled Van Persie out for a month following the 1-0 win over Arsenal in early November. Moyes admitted he might have taken the player off earlier during the striker's comeback match, the defeat by Newcastle, but denied the Holland striker was rushed back early. "No, not at all," he said, who introduced Van Persie as a 63rd-minute replacement against Shakhtar as United pushed for the win. "We could have played him [before in that game] but we actually decided not to because I spoke to him and we'd played him probably just too much.

"It's a blow because he's so influential, the goals he's got. If you think about the games that have been tight, even in the last week or so, last year he was the one who was nicking the winner in a lot of those games."

Van Persie's absence means an even greater onus on Wayne Rooney, who will play his 500th career game at Villa. Asked if there is a fear of the England striker burning out, Moyes said: "Strangely enough the idea slipped out of my mind because he'll have to play the games for us and we'll use him as much as we can."

Moyes did admit that, before Van Persie's injury, he might have rested Rooney. "That would have been a consideration for us but obviously not having Robin just now we can't think that way," he said.

Regarding a new deal for Rooney, whose contract expires in 18 months, Moyes added: "The club are comfortable, there are lots of discussions between the club and his representatives so I think that's all fine. I don't see any great panic or great rush."

The manager added that Michael Carrick is still around two weeks away from returning from an achilles problem, with Nemanja Vidic and Patrice Evra (both with knocks), Marouane Fellaini (back) and Chris Smalling (hamstring) also out.