In January 2014, it was Matic who was the subject of a £21 million transfer from the Portuguese capital to Stamford Bridge. This time he would have an instant impact, dominating Yaya Toure on his first start since rejoining the club in a memorable 1-0 win at Manchester City. Fast-forward another three and half years and it seems his time in West London has drawn to a close with a £40m transfer to Manchester United reportedly all but sealed.

Assuming the reports are correct, the Serbia international will leave Chelsea this summer decorated with two Premier League winners medals along with one from the triumphant 2015 Capital One Cup campaign despite being suspended for the final. The collection is vindication for Jose Mourinho's decision to bring him back to the club for a transfer fee several times in excess of the one he was sold for in the first place. Now Mourinho is seeking to sign Matic for a second time and for an even more extravagant price. It begs the question, therefore, as to whether Chelsea are wise to sell him at this juncture, especially to a direct rival?

Matic divides opinion among Chelsea fans. Some see him as the physically dominating midfield presence that allows the more diminutive players in the team to thrive. Others see him as a clunking midfielder whose lack of creativity inhibits the team's passing game, particularly in matches in which possession is controlled by the opposition. Both opinions have validity and each has its root in his erratic form over the last few seasons.

Having bossed Man City's midfield upon his return, Matic went on to be the most effective midfield enforcer in the Premier League over the next 10 months, with Chelsea soaring away at the top of the table by the start of December 2014. But then his impact diminished enormously. It was not in isolation, the whole team's swagger was checked by the 5-3 defeat to Tottenham on New Years Day, but his sudden inability to shield the artistry of Cesc Fabregas alongside him meant that Chelsea crawled to a title that they should have cantered towards.

2015-16 saw almost the entire squad struggle, though his inability to stamp his mark on the centre of the pitch was at least as damaging as the toils experienced by Diego Costa and Eden Hazard. That brought the first murmurs of dissatisfaction from Chelsea supporters, although he was far from alone in being targeted.

Last season saw a mix of all of the above. There were times when Matic was utterly imperious, bestriding games with the superiority implied by his physical stature. But then there were others -- notably the 2-0 defeat to Tottenham in January and the FA Cup final disappointment against Arsenal -- in which he was bypassed so often that he became a virtual bystander.

The true Nemanja Matic is somewhere in between. More gifted on the ball that most suspect but less imposing than many would wish. He can carry the ball forward with authority yet can also cede possession by failing to execute a simple short pass. In many ways he is both misunderstood and underrated but that does not mean that Chelsea should not cash in on him this summer.

A £40 million fee, even in these days of Premier League largesse, is not to be sniffed at. With Chelsea supposedly targeting the likes of Juventus' Alex Sandro, Southampton's Virgil van Dijk, Everton's Romelu Lukaku and Monaco's Tiemoue Bakayoko in what would be a spending spree in excess of £200 million, such a large receipt would be gladly welcomed.

Matic's departure would also enhance the prospect of Nathaniel Chalobah being more fully integrated into the first team picture following an impressive summer with the England U21s. Bakayoko's arrival would obviously present a similar barrier to the academy graduate's progress, but with Champions League football providing a congested fixture list and demanding full use of the squad, Chalobah now has a greater chance of featuring more regularly.

Of course, Matic moving to a major rival and potentially strengthening them does sit a little uncomfortably, though, if Chelsea want to sell to the highest bidder, there are few other options now that China's clubs have been slapped with an onerous tax on overseas players. The influx of astronomical amounts of television money means that Premier League clubs are now the apex predators in the transfer market.

Crucially, this isn't a case of Chelsea seeing their best players picked off by other clubs. This is a straightforward business decision of realising the best return for an asset that is no longer considered integral to the team's success. It might sound cold when referring to a double Premier League champions but football is a ruthless endeavor.