Sir Alex Ferguson is to step up his search for a player in the image of Roy Keane after two years of frustration.

The Manchester United manager admits "it is not easy" replacing the midfield enforcer, now plying his trade at Celtic.

Ferguson said: "We have been looking for a Roy Keane replacement for over two years and nothing has changed.

"Trying to identify that type of player is not easy. But I can assure you there is a big urge to scour the market for someone suitable."

While Ferguson has come up against a brick wall in his bid to find the new Keane, he believes his two defensive recruits can make a big impact at Old Trafford.

Nemanja Vidic and Patrice Evra arrived last month for a combined #12million.

Ferguson said: "I wanted to improve our cover during the January transfer window, so I am delighted with the two acquisitions.

"We have been watching Evra and Vidic for a while now. Obviously, with the injury to Gabriel Heinze our move for Patrice accelerated quite a bit because we were in desperate need of someone to fill that position.

"The next area to tackle is the midfield."

Ferguson believes United can now match runaway leaders Chelsea when it comes to getting positive results.

"It is frustrating to see their position in the league but we have to give them credit for how good they have been," he told the Manchester United magazine.

"Our points total is the best it has been at this stage of the season for about 10 years.

"So we can only applaud the consistency Chelsea have achieved. I have no doubt we can also achieve that consistency.

"Unfortunately there is no guarantee of clawing back Chelsea's lead as they are unrelenting.

"They defend really well so you cannot see them losing many games."

It was United's early season form that left them playing catch-up, according to Ferguson.

"The injuries we had did not help and that's when we had our worst set of results, " he said. "Once we started to get players back our form improved dramatically.

"Generally I am happy with the way we are progressing. We have a lot of young players but it is important we do not start setting standards too low.

"We have to make them aware every game is important to us. I am sure they realise that anyway so motivation should never be a problem."