Manchester United have been resigned to losing Nemanja Vidic for some time –Internazionale have been strongly linked with the defender since he indicated last month that this would be his last season at Old Trafford – so confirmation that he will move to Milan in the summer does not amount to a surprise.

David Moyes has a decision to make over whether he allows the player to retain the captaincy in such circumstances, though the loss of a 32-year-old centre-back beginning to show signs of his age and his struggle with injuries should not disturb United unduly. If anything it takes the uncertainty out of the situation and leaves Moyes free to begin looking for a replacement, although when the subject arose on Vidic announcing he would leave, the United manager said he was quite happy with the options he already had at the club.

Sir Alex Ferguson always said United were well off for centre-halves, with Phil Jones, Jonny Evans and Chris Smalling all available as understudies to Vidic and Rio Ferdinand, yet the number of times Michael Carrick has been pressed into service as a central defender is an indication of how often many of those players have been injured or suspended at the same time. With Ferdinand three years older than Vidic and even more infrequently spotted this season, there is a shortage of experience once the two senior defenders are removed from the equation, and while Jones, Evans and Smalling all have ability and potential there is a feeling among United supporters that a more authoritative leader is required at the back.

Vidic has performed that role admirably in his eight years with United, either as half of a regular partnership with Ferdinand or as the example for one of the younger players to follow. Few opposing forwards have got the better of him, though at one time Fernando Torres appeared to have the ability to reduce him to a nervous wreck, and in a similar fashion to John Terry at Chelsea, Vidic also had the useful knack of imposing himself in the opposition's penalty area, when his determination to reach free-kicks and corners would often result in an important goal.

It is not too hard to work out why Vidic is looking to Italy to prolong his career. The game is slower and more thoughtful in Serie A, and a player with Vidic's positional sense and strength should be able to last a few more years at the top. He had already made up his mind to leave the Premier League by the time he earned his last suspension in January for a ridiculous lunge at Eden Hazard in the closing minutes of United's defeat at Stamford Bridge, though that brief indiscretion encapsulated for many why the defender's days in English football were numbered. Chelsea are the coming team under Mourinho – he has them playing at an astonishing pace so as to turn defence into attack almost instantly from any part of the pitch, whereas United under Moyes look cumbersome, predictable and old-fashioned.

That is not a particular criticism of Moyes, the best teams could make Ferguson's United look like that too. It just happens that ageing centre-halves are always susceptible to pace and it already seems clear that Chelsea and Manchester City are going to be the leaders in that area for the next few seasons.

Vidic's contribution to United's ongoing success was as immense as some of his defensive performances and at the end of the season he will leave with most people in Manchester's best wishes. While there can be little doubt he has given his best years to Old Trafford, the extent of Inter's gratitude at his capture was almost touching. "Vidic is a great champion, one of the strongest defenders in the world," the club president Erick Thohir said. "He will add value to the club and will be another pillar for the construction of a great Inter."

No pressure then. If anyone can cope with that billing the former Red Star and Spartak Moscow defender can, though it seems only fair to point out that English clubs in the habit of buying thirtysomethings whose prime years had been spent abroad always used to be told they needed to sign them 10 years earlier to be taken seriously. United did that with Vidic – they went out and found a player to give them the best part of a decade of solid service.

He remains one of the best of Ferguson's post-treble signings, and if he now falls into the classification of cast-off, you wouldn't want to be the one to tell him to his face. One way or another United are now charged with replacing him, either in-house or via the transfer market, and that, as Moyes is doubtless starting to realise, will be no straightforward task.