Chelsea begin the defence of their Premier League title on Saturday when they welcome Sean Dyche's Burnley to Stamford Bridge.
John Terry ended his 19-year stay at the club by lifting his fifth league trophy, and following his move to Aston Villa, Gary Cahill is the man Antonio Conte chose to take over as captain.
The England international made 43 appearances last term, weighing in with eight goals, but no one was more prolific for Chelsea in the 2016-17 campaign than Diego Costa.
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The ex-Atletico Madrid centre-forward top scored for the Blues with 22 goals in all competitions, including 20 in the Premier League and one in the FA Cup final.
Despite recapturing his very best form under Conte, the Italian manager informed Costa that he is no longer a part of his plans, and Cahill has warned his club about selling their star striker.
Morata in, Costa out?
At the start of the summer, it was revealed that Conte told Costa via text message that he had no future in west London and should look for another club.
The Premier League champions then went and signed forward Alvaro Morata from Real Madrid for a club-record fee believed to be around £60 million.
Cahill warns Chelsea about selling Costa
New skipper Cahill has been discussing what Chelsea will miss were Costa to leave this summer, saying, via The Mirror: "Diego Costa is Diego Costa. He scores goals."
"He is an animated character and he is a big personality," the 31-year-old continued, before appearing to confirm that Costa is on his way out of the club.
"He will be a big miss. We have obviously added to the squad with Alvaro (Morata), and that is a great addition to the squad, but you are always to going miss big players.”
Should Chelsea sell Costa?
Costa reportedly wants to return to Atletico, for whom he scored 64 times between 2010 and 2014, but their transfer ban is proving to be an issue.
Given the fact that the 28-year-old is a proven Premier League goalscorer, many people have questioned Chelsea's decision to let him go in this transfer window.
On the other hand, his replacement Morata scored more goals for Real last season than Karim Benzema did, despite his lack of game time.
The 24-year-old Spaniard has been crying out for regular first-team football for years, and maybe will see the very best of him at Chelsea following his big-money move.
Do YOU think Chelsea should sell Costa this summer? Do YOU think he will actually leave? Leave YOUR opinion in the comments box below!