Patrice Evra is currently in the midst of a true renaissance season.
He has improved his defensive frailties of the past while also becoming a far more potent attacking threat down his favoured left wing.
But at 31 years of age, the Frenchman may only have a couple of good seasons left in him before tired legs begin to take over.
Sir Alex Ferguson may already be considering who he wants to replace Evra in the long term, with a host of candidates having been linked to the club or those already playing in the red of United.
Here are the five most likely options at the time of writing.
Alexander Buttner was bought from Vitesse Arnhem in the summer to primarily serve as a back-up to Evra.
Though much was expected of him at the time, hopes for the young Dutchman have since cooled a little as he has found playing time difficult to come by.
Buttner has looked promising while playing for the reserve team this term, but serious doubts remain over just how high his "potential" ceiling is.
A loan spell away from Old Trafford may be the best option for a player who is in need of high-quality, first-team action. Only time will tell.
Yuto Nagatomo is a name that has only very recently been linked with Manchester United.
Click Manchester, a local website, reported that Sir Alex Ferguson was plotting a summer swoop for the Inter Milan full-back a week ago, with scouts already dispatched to Italy to monitor his progress (h/t The Express).
The Japanese international has blossomed into a regular member of the Nerazzurri since moving from AC Cesena in 2011, and he might be an expensive signing because of his importance to the Serie A side.
He is renowned for his exceptional work rate and versatility. He can play on either flank as well as in midfield and has an excellent attitude to the game.
For a brief time this past summer, there was a genuine debate raging between many Manchester United fans over who the club should sign at left-back.
The Welshman recently signed a new contract extension with Michael Laudrup's side, but that doesn't mean his club wouldn't be tempted into selling were a significant offer to be made.
Taylor is technically capable of playing at Old Trafford, but having suffered a broken ankle in a game against Sunderland earlier this season, there might be doubts over him being a little too lightweight.
Fabio has had an up-and-down time at Queens Park Rangers during his loan spell for the London club this term.
He has been rotated in and out of a first team in the midst of a torrid relegation battle—hardly a conducive environment for a young player to develop.
His twin brother Rafael has improved immensely for the Red Devils meanwhile, becoming a reliable mainstay in the back four and a promising attacking threat.
Though he may have now slipped a little behind in terms of development, Fabio could still eventually earn a place on the opposite flank to his sibling. Some even consider him the more naturally talented of the two.
Finally we come to Leighton Baines—the true No. 1 contender to eventually dethrone Patrice Evra as Manchester United's first-choice left-back.
Rumours about Sir Alex making a move for the talented England international first sprung up early last year, but even now such stories are yet to dissipate (via Daily Mail).
The Daily Mail recently reported that he remains the Scotsman's preferred choice, but Everton's £15 million valuation has, as yet, kept a transfer from taking place.
With Baines improving with every game, though, that price tag is unlikely to be lowered as the notoriously tight Blues seek to hold on to one of their stars.
Who do you see eventually replacing Patrice Evra at Old Trafford? Are any of your candidates not on the list?