Oscar's dramatic decline at Chelsea accentuated by rise of Juan Mata

The Blues may not have been in scintillating form themselves of late but continue to scrape together narrow wins to strengthen their position at the top of the league. With Arsenal up next weekend for Jose Mourinho's men, Louis van Gaal's Red Devils have a real chance to put pressure on the Londoners with a win on Sunday.

WhoScored.com look ahead to the weekend battle and in particular at the contrasting fortunes of the No. 8 on either side.

At the start of the season, Mourinho's mind seemed to be made up as to his best XI. Cesc Fabregas would play alongside Nemanja Matic in midfield, with Oscar given the role in behind lone striker Diego Costa. The Brazil international would register four goals and five assists in the Premier League before the New Year and began 2015 with a further two assists and three league strikes, culminating in a brace in Chelsea's 5-0 win at Swansea in January.

A 4-2 shock humiliation at the hands of Bradford would follow and ever since that upset the Blues have failed to win a single game by more than a solitary goal. Oscar, meanwhile, has seen his impact and playing time wane thereafter, failing to contribute to a single goal across all competitions since that rout at the Liberty, making 13 appearances in that time.

While the 23-year old has been featuring in most matches, he has played just 765 minutes of the 1170 possible in his league and Champions League appearances this year (65.4%). Compare that to 1497 minutes from a possible 1800 across the same two competitions in his 20 appearances prior to New Years' Day (83.2%) and it's clear that Mourinho's previously unwavering faith in the youngster has diminished.

It was, after all, Oscar's superior defensive work rate that was deemed a major contributing factor to the Portuguese's willingness to sell back-to-back Chelsea Player of the Year Juan Mata, to league rivals United no less. The Chelsea man has just two statistical strengths according to WhoScored.com, one of which is his 'defensive contribution', while Mata has as many as nine, along with three weaknesses, one of which is indeed his 'defensive contribution'.

Nevertheless, the likeable Spaniard will return to the Bridge for the first time this weekend in confident mood, rightly feeling that he has a point to prove to his former manager.

While Oscar's future at Chelsea now seems insecure, Mata is beginning to flourish at a time when United are undoubtedly playing their best football of the season. The 26-year old may have played slightly fewer minutes in the league than his old team-mate this season but, for now at least, seems to have convinced his new manager of his worth in the starting XI, struggling to do so at the start of the campaign just as he did when Mourinho returned to Chelsea.

Mata has still managed to score eight league goals this season, along with four assists, and has hit form just in time for his return to West London, having a direct hand in four goals in his last three appearances. Indeed, the only two midfielders with a better WhoScored.com rating in that time (8.28) are Eden Hazard and Ander Herrera, so it's clear that there will be a number of players on display at the top of their game.

By comparison, Mata's opposite number at Chelsea has failed to pick up a rating in excess of 7 in his last seven appearances in all competitions. The fortunes of the two have very much turned on their head and the same can be said for the clubs to some degree. There's no question that United are playing the better football of the two right now - which would have been unthinkable before the turn of the year - and this weekend, in Mata, they may well have a man on a mission.