5 Unsung Chelsea Heroes Jose Mourinho Must Keep in Summer Transfer Window

Chelsea are Premier League champions, and while Jose Mourinho's men have been the standout team in England this season, that doesn't mean the Chelsea boss will rest on his laurels.

If anything, it means the opposite.

Over the summer, Mourinho will be making plenty of changes with his squad, making tweaks throughout to ensure he can keep Chelsea ahead of the chasing pack.

As well as players coming in, it will mean some inevitable departures as the club look to balance the books in line with financial fair play.

Alongside the more celebrated names such as Eden Hazard and John Terry, Chelsea have called upon some unsung heroes to see them over the line this season.

With a busy summer ahead, Bleacher Report identifies five key players who should be among Mourinho's untouchables when he considers who to sell this summer.

Gary Cahill

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Gary Cahill has been the real success story of Chelsea's shrewd transfer dealings in more recent times.

Signed for just £7 million from Bolton Wanderers in 2012, he has gone on to win every major honour in England and Europe in just three years.

He hasn't done that by sitting on the bench and being a glorified cheerleader, either.

Cahill has been a major part of the success Chelsea have enjoyed, forming a strong partnership with John Terry.

Indeed, it is his emergence that allowed Chelsea to cash in on David Luiz when they did—Cahill ousting the Brazilian as Terry's preferred partner.

A tricky Christmas period this season raised a few doubts about Cahill, but he's rediscovered his best form and is a major asset for his club.

With just Kurt Zouma as cover, there's an argument to suggest Chelsea need to add another centre-back to their squad.

If they do, it shouldn't come at the expense of Cahill.

Willian

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Tottenham Hotspur were kicking themselves when they allowed Willian to slip through their fingers and sign for Chelsea in the summer of 2013.

The Brazilian was all set to join the White Hart Lane club when Chelsea nipped in at the 11th hour to take him to west London instead.

Two years on, Spurs chairman Daniel Levy must be regretting it even more given what a success story Willian has proved to be.

Willian is an integral part of this Chelsea team, and without him operating on the right flank, Chelsea do lack the same intensity he brings.

When Juan Cuadrado joined in January, the consensus was that the Colombian would be challenging Willian for a starting place.

Not only has Cuadrado disappointed, he hasn't come close to challenging Willian, simply because the Brazilian has been magnificent.

Eden Hazard rightly gets the plaudits in attacking midfield, but we shouldn't let that take away from Willian's magic.

Branislav Ivanovic

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Strangely, Branislav Ivanovic has a Marmite effect on Chelsea fans—they either love him or hate him.

That's tempered by the fact he is keeping Cesar Azpilicueta out of his preferred position at right-back but also because he can at times leave Chelsea exposed.

Ivanovic likes to get forward and join attacks—too often for some—and it can isolate Gary Cahill.

That said, you'll be hard-pressed to find a better defender in the Premier League in his position.

Ivanovic contributes plenty, proving an asset at set pieces and adding a bit of steel to the rearguard—a quality Jose Mourinho will no doubt appreciate.

Not only that, he is good for a goal, with some of his strikes coming at vital times.

Ivanovic is 31 now, so he's ageing, but those legs have plenty more games in them.

Filipe Luis

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It's been a frustrating debut season at Chelsea for Filipe Luis.

He joined the club from Atletico Madrid with a considerable reputation and was expected to take over the left-back slot from Cesar Azpilicueta.

That hasn't happened, with Azpilicueta proving just as good this season as he was last, when he ousted Ashley Cole from the Chelsea team.

Luis has still played his part, however, proving a big figure in some key matches in which he has featured.

The Brazilian gives Chelsea a solid look at left-back, ensuring there is plenty of cover in a key part of the pitch.

Given Chelsea's streamlined reserves elsewhere at the back, it's vital they keep him this summer.

That could be easier said than done, however, with the Evening Standard reporting that Luis could be on his way back to the Vicente Calderon Stadium.

Loic Remy

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Another player who has endured a frustrating first year at Chelsea is Loic Remy, although the Frenchman's angst has been for different reasons to Filipe Luis.

Remy has suffered injuries at key times this season, and it's meant him missing large spells.

First it was a groin injury in October when he was hoping to make the most of Diego Costa's injury problems, while more recently a calf problem meant he missed most of April.

Remy has scored some vital goals this season, though, notably the winners against Hull City and Stoke City in March and April.

Those goals went a long way to helping Chelsea seal the Premier League title.

Not only that, they outlined Remy's quality and proved he is the perfect foil to Costa.

Chelsea are expected to be replacing Didier Drogba this summer, with age finally catching up with the Ivorian. If that's so, Remy's presence ensures the Blues should be in the market for just the one front man.