Marouane Fellaini knows "he can play better" for Manchester United, according to David Moyes, who is convinced the £27.5m signing is slowly settling into his role at the club.

With Phil Jones and Michael Carrick both injured, Fellaini should start in Sunday's visit to Cardiff City alongside either Tom Cleverley or Ryan Giggs in central midfield as Moyes faces up to a mini-crisis in that department, with the disappointing Anderson his sole other recognised player in the position.

"[For] a lot of people who join Manchester United – it doesn't always happen as quickly as you would like," the manager said of Fellaini. "He needed to take time but we threw him in very quickly. Ideally we would have bedded him in more gently and at the right opportunities. But we had to put him into some big games at quite a difficult time for us."

While Moyes was referring specifically to Fellaini starting in United's 4-1 derby humiliation at Manchester City in September, the manager stated the Belgian understands he needs to improve. "He knows he can play better," Moyes said. "When he came into the team we were not playing as well as we would have hoped. I think we are yet to see him properly. He can be a bigger influence. There have been a couple of games where I thought he threatened to be a big influence.

"I thought in the opening part of the game against Shakhtar Donetsk in Ukraine [a 1-1 Champions League draw last month] he was an influence and made the goal for Danny Welbeck.

"There have been moments where he has threatened to become that big influence. I think maybe being booked in some of the games has taken a bit of that away but there have been signs. He will be fine for us."

Fellaini's need for a surgery in the new year may also be a factor. "He has a wrist injury that we know he is going to have to have an operation for," said Moyes. "I think it is a little bit that he is protecting it. We are wary of that."

Moyes hopes that once in top form Fellaini can contribute goals. "We played him much higher up the field at Everton which meant he scored a few," he said. "We are hoping that he is going to score a few here. He's had a few goals in him as either an attacking midfielder or coming from deeper and that was one of the reasons he appealed to us because he can get goals for us."

With United five points behind Arsenal, Moyes is conscious that the busy period up to January may be vital to the champions' title defence. "Yes it could be a defining period if you don't keep up with the Jones's," he said. "But in the same breath there are a lot of clubs who'll be saying they have to keep up with us as well. We are in good form."

While Jones's groin injury means he has a chance for Wednesday's Champions League trip to Bayer Leverkusen, "possibly", Nemanja Vidic, who is recovering from concussion, and Rafael Da Silva's ankle problem, means each is a doubt for Cardiff.

Welbeck, who is also ruled out with a knee injury, does not require surgery. "No operation," said Moyes. "He is back training. It is a little bit of a concern [the injury]. He has done a lot of work on strengthening the muscles around his knee to try and make sure it prevents it. It is more injury prevention as much as anything."

Moyes is, however, buoyed by Darren Fletcher's steady progress as he battles a chronic bowel condition. "He is not quite ready yet. He has a bit to do yet in terms of more reserve games and a little bit more time," said the manager. "It is great to see him out training regularly. That is a big thing. He is beginning to look like a footballer again.

"I wouldn't want to put a date on a comeback because of the illness he's had, it is just something we have to take as we go along. He is training well. He is looking good and we will try and keep that continuing. I wouldn't want to put a date on it because I would have to check with the doctors that everything is going to plan."