Manchester United Paying Price for Not Replacing Nemanja Vidic and Rio Ferdinand

It should have been little surprise that, with a combined age of 67, Rio Ferdinand and Nemanja Vidic were coming to the end of their time at Manchester United.

After spending eight-and-a-half years at the heart of the defence, they didn't owe United anything. They left Old Trafford after a combined 755 appearances and 21 major trophies.

At 35 years old, it was probably the right time for Ferdinand to move on. United might have gotten another couple of years out of Vidic, but he announced his decision to leave in February, giving the club plenty of time to decide how to react.

They didn't. Not properly.

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Ferdinand and Vidic have gone. On Saturday, when West Ham visit Old Trafford, Louis van Gaal will have to pick a makeshift back four made up of inexperienced youth-team players and fresh-faced new signings.

Sir Alex Ferguson might feel he left ready-made replacements for Ferdinand and Vidic when he retired. However, Van Gaal won't have the use of the injured Jonny Evans, Phil Jones or Chris Smalling against West Ham this weekend.

Fans will say it's not a great surprise, with the careers of all three having been interrupted by layoffs at different times. United were confident in the summer that Evans, Jones and Smalling had returned to pre-season training as fit as they'd ever been.

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But it's not even October and they are all on the sidelines. Evans and Jones could yet be out for a month.

Van Gaal has added Marcos Rojo from Sporting Lisbon and Tyler Blackett from the youth team. While they might have replaced Ferdinand and Vidic in terms of numbers, it's not clear yet whether they'll ever possess the same quality.

The injuries to Evans, Jones and Smalling are unfortunate, but the situation has only served to emphasise United's lack of depth at the back.

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It seems strange that, after a summer when they have spent more than £150 million on new signings, United will have to call on two youth-team players, Tom Thorpe and Patrick McNair, to fill a void at centre-back after only six games of the new season.

There is little Van Gaal can do about it now. He will have to wait until at least January, possibly even next summer, to get the targets he wants.

Nevertheless, Ferdinand and Vidic will need to be replaced eventually, and sooner rather than later.

If Van Gaal starts to doubt whether he needs reinforcements at the back, he need only remember the difficulty he had trying to assemble a back four to play West Ham in September 2014.