David Moyes insists that Rio Ferdinand remains a key player in his plans as Manchester United manager despite not selecting the defender in the match-day squads for the past five games.

The 35-year-old started United's 1-0 defeat of Shakhtar Donetsk in the Champions League on 10 December but has been left out since and, while Moyes said Ferdinand has had problems with a calf, it is understood that these are minor.

"He's had a few injuries, a few niggles in his calf, but overall Rio's very much a part of it," the manager said before Wednesday's Wednesday teatime home game against Tottenham Hotspur. "The form of the team and the form of some of the young players has meant I've not needed to look to change it around too much."

In the absence of the veteran, whose long-term future at United remains in doubt as he is yet to be offered a fresh one-year deal, Moyes has selected Chris Smalling and Jonny Evans as his central defensive pairing. This has meant Nemanja Vidic, the captain, has also sat out games, though he did start United's 1-0 win at Norwich City at the weekend.

Moyes said he is not afraid to leave any player out. "That's part of the job and, if you play for this club, you always know there's going to be competition for places. I think if you manage this club there are always going to be big decisions to make.

"I think the players here all play their part. Rio and Vida have been two of the best centre-halves, certainly in this Premier League generation.

"For the last 10 years they have been terrific, so overall they are still very much a part of it. We'll continue to use them. There have always got to be other people to come in. This club has always got to have a line of people who are ready to come in and take their places and push them, and I think even for the young players, the challenge is to push the old players and take over. That's the way it works."

With the champions eight points behind Arsenal, Moyes admits he has a rebuilding job to do though this will not occur in the January transfer window. "I think [if] Sir Alex [Ferguson] was still here, he would have said they would have needed to be a rebuilding job, but it's a continual rebuilding job going on here all the time. We're always looking to the academy first and foremost, asking whether we can bring young players through from there, who are the next ones possibly coming up to the first team? That's the first thing we look for. After that, we'll go out and look and see if we've not got a position covered, then we'll try to find someone out there better than what we've got or to push what we've got it."

Asked whether he would be relaxed not to sign any players in January, Moyes said: "I don't know if I'd use the word 'relaxed'. I would say that I'd like to do something and I will try to do something. We'll try and we'll try to get close to doing things if they're possible."

Robin van Persie is not yet available due to a thigh injury and Moyes said Wayne Rooney is a doubt because of an adductor strain. "We'll need to wait and see. He didn't train, so we'll assess it tomorrow and see how he is."

Moyes also denied that Van Persie was proving susceptible to injury. "He's not proved vulnerable to me, I think he's been fine. People do get injuries. If you look at other clubs in the country, they've got important players injured, so it's no different. But he's important to us and, if we can get him back, great. And when we do get him back we're looking forward to trying to keep him fit and healthy and ready to play. Wayne's not trained today so we'll have to wait and see tomorrow."