One cost £30m and is the new England captain, the other is rated in the £20m bracket and was United's Player of the Year last season.

But two cost-nothing homegrown talents have shaken up the defensive order at Old Trafford.

Fabio Capello's new World Cup leader Rio Ferdinand and Real Madrid and Barcelona target Nemanja Vidic have been the bee's knees since 2006.

But injury has forced the pair out this campaign and Jonny Evans and Wes Brown, both reared in the Reds youth system, have grasped their opportunity.

Though Sir Alex Ferguson had already touted Northern Ireland international Evans as Ferdinand's eventual successor and Mancunian Brown has been a senior at United since 1998, the task of breaking up the incumbent Anglo-Serbian axis looked an impossible one.

Ferdinand and Vidic provided the backbone of three successive title campaigns and back-to-back Champions League finals, including Moscow triumph of 2008.

It was recognised as the sturdiest partnership in Europe.

But 31-year-old Ferdinand's thigh, back and calf troubles - and current suspension - plus Vidic's torment with a nerve problem, has meant between them they have missed a combined total of 46 matches this term.

The pairing has only started seven matches.

Former United defender Gordon McQueen believes the Ferdinand-Vidic double act will be restored, but that their grip on the role has been severely loosened.

"For the last couple of seasons we have been asking whether Rio and Nemanja was a better partnership than the hugely successful Steve Bruce and Gary Pallister pairing," Gordon told M.E.N. Sport.

"We've been debating its merits as the best in Europe and even the world. I still think that when they are fit and available Sir Alex Ferguson would match them up again.

"I think they will be back and forming a solid on-field relationship again. But United and, significantly, the two players know that there are players who will push them all the way and are a proven pairing in their own right.

"Wes is an England international and Jonny is one of the most highly-rated centre-backs in British football and probably Europe.

"The pecking order might not be so cut and dried anymore. It is no longer set in stone.

"I remember a time when I was at Old Trafford and for a while if ever I was out injured for two or three matches I would always get back into the side once fit.

"But then the likes of Kevin Moran and Graeme Hogg started to step in and prove themselves and me returning was no longer so certain. I knew I had a scrap on. I had to look over my shoulder.

"There is no doubt that Ferdinand and Vidic are facing that same uncertainty now. They cannot consider themselves definite starters when fit anymore."

Ferdinand's back troubles and rumours that Vidic is being coveted by La Liga's Big Two also put the cat among the pigeons.

"I don't think Rio's injuries will have a big impact. I think he's over them now," Gordon added.

"As for Nemanja, I just cannot understand why anyone would want to leave Old Trafford.

"I can maybe accept a Spaniard wanting to return to Spain. I can grasp, for instance, why Cesc Fabregas might want to leave Arsenal for Barcelona.

"But I don't get why a Serbian would have any pull to go elsewhere. Would Vidic have more success in Spain, I don't think so. Would the style of football be more satisfying, I don't think so. I just don't get it.

"However, I believe if he is still part of Fergie's plans then he will be at United next season."

The United boss has already put in motion plans for the future of the centre-back department by capturing Fulham's Chris Smalling during the January transfer window.

The England Under-21 defender is back at Craven Cottage until the summer and will become a Reds player for next season.

McQueen knows all about Smalling's qualities - he recommended him to Middlesbrough when scouting for the Riverside club.

"Chris went to Middlesbrough and had agreed to sign when Fulham came in late and he decided he'd be homesick on Teesside," added Gordon.

"He's got a bit to learn and is one for the future. He is a tremendous prospect. He is very much in the Rio Ferdinand mould.

"He has all the attributes to make it to the very, very top because he is mobile, quick and athletic."