Manchester United were pipped to the title on the final day of last season by bitter rivals Manchester City, relinquishing their stranglehold on the league in the process. A key part of manager Sir Alex Ferguson's gameplan last term was the blooding in of several younger faces, yet the Da Silva twins - Fabio and Rafael - still both struggled for time on the pitch. It begs the question, when will they ever break into the starting eleven?

Liverpool clinched the signings of Florent Sinama Pongolle and Anthony Le Tallec in a joint deal back in 2001 from French club Le Harve to much fanfare, reportedly beating off competition from the likes of Juventus and Barcelona in the process after the pair sparkled in the European U-16 Championships and later the U-17 World Championship. At the time, the move was heralded as something of a transfer coup, beating some of Europe's elite to the signatures of two of its hottest prospects.

However, while at Anfield, they failed to make the grade in the first-team despite their reported huge promise. They were shifted about on loan to various countries in an attempt to grant them the first-team opportunities that they were being deprived of at their parent club before finally being allowed to move on, with Sinama Pongolle moving to Spanish side Recreativo in 2006 and Le Tallec ending up at Le Mans in France in 2008.

I think it's fair to say that both struggled to live up to the hype and while the Da Silva twins are clearly players of more potential and greater quality, you have to wonder if the two situations are in danger of mirroring themselves with both players being linked with loan moves away this summer.

The Manchester United defence isn't in the best of shape. It's sure to be bolstered by the return of club captain and all-round hard egg Nemanja Vidic, alongside either Jonny Evans or Rio Ferdinand in central defence. Then, of course, there are the likes of utility defenders Chris Smalling and Phil Jones, while Patrice Evra firmly remains the club's first-choice left-back.

Nevertheless, the defence is in more of a state of flux than in years gone by; these are transitional times for the United back four and, you would think, the ideal period for both the Da Silva twins to make their mark, but a series of niggling injuries and penchant for the treatment table have seriously hindered their progress in recent years.

Manchester United have been heavily linked with a move for Everton left-back Leighton Baines this summer, which would indicate that Ferguson has finally cottoned on to the significant drop in performance of Evra over the past year or so. This would indicate two things - firstly, that the club are in the market for a new left back and long-term heir to the Frenchman and secondly, that Ferguson simply doesn't trust Fabio yet.

Rafael battled gamely with John O'Shea the year before last for the right-back role and with the Irishman having surprisingly been allowed to move to Sunderland at the beginning of last season, the spot was there for the taking, but he went on to make just 18 appearances in total last term and you have to wonder if his chance has now passed, more by circumstance as opposed to any real fault of his own.

They both clearly have fantastic potential - energetic, committed (sometimes too much) and with an excellent work-rate - the only thing really missing is the fact that they lack positional discipline, which is something that's easily solved the more that they play, but they've made just 44 league appearances between them in the last two seasons.

Injuries have hugely restricted their development at a crucial time in their respective careers. Now should be the time when we are talking about how settled the side are when it comes to the full-back positions for the next decade or so, particularly when you consider their age, but it still hasn't happened yet.

Ferguson has utilised the loan market to his benefit in the past, with Danny Welbeck at Sunderland and Tom Cleverley at Wigan both earning rave reviews playing week-in, week-out which granted them the platform to push on once they returned to Old Trafford, and the Da Silva twins are more than capable of doing the same.

However, with both Welbeck and Cleverley, you could understand why their route into the starting eleven remianed blocked for the time being, considering the established players and depth of talent that they had in front of them, but that simply doesn't apply to Fabio and Rafael.

The French pair of Le Tallec and Sinama Pongolle were expected to achieve great things at Anfield but ultimately, they not only fell well short, they were cast by the wayside and there remains a very real worry that Ferguson is beginning to see a future beyond the talented Brazilian twins, instead choosing to cast his eye elsewhere at more reliable and durable options. If they manage to stay at the club next season, it will remain the biggest of their careers, for even the word 'potential' has an expiry date on it.

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