The story of Diego Costa's hamstring just isn't going to go away. After an injury-punctuated debut season in English football, where he scored a creditable 20 Premier League goals in 24 matches, there had been a belief the summer lay-off would cure all.

Through a mixture of rest and surgery, the expectation was that the injury that has been looming over every minute the Spaniard has played since his move from Atletico Madrid to Chelsea, would be gone.

But with Costa being omitted from Sunday's FA Community Shield, there will be a very real worry that the coming season will bring more of the same. The truth, at the moment at least, is that we really don't know how much of an issue the key tendon in the forward's leg will be.

Jose Mourinho's decision to leave him out of the season-opening showpiece was largely precautionary.

A clear message was sent from the technical area in the form of the Blues' boss' attire – casual, compared with Arsene Wenger's formality.

It could be argued that also translated into a lot of Chelsea's play, notably for defending that led to Alex Oxlade-Chamberlain's goal, which was particularly dress-down-Friday.

And thus, with next weekend's visit of Swansea City to Stamford Bridge nicely framed by Mourinho as the bigger of these two games – Costa was always going to be rested here. The main issue with that is the two other men in Mourinho's cannon, Loic Remy and Radamel Falcao, are largely unknown quantities.

Remy, who himself had a season strewn with injuries and a lack of match fitness in 2014-15, has an enviable record when he does play – with a minutes to goals ratio for Chelsea that is among the best in the league. But against Arsenal he looked well off the pace, and alarmingly found himself offside five times in 45 minutes – not something Mourinho would expect to see in a top striker.

Falcao, of course, is a compete random punt – though, again here, Mourinho will insist there is less chance in that acquisition than on first glance. He is certain he can return a great striker to top form, and presumably part of the lure for the player (aside from the fact few clubs can afford his wages), is the promise he will get game time due to Costa's predicament.

Chelsea, of course, managed to win the league last season with Costa missing more than a third of games. And the only backup they had was that infrequent assistance from Remy, and a Didier Drogba tribute act that seemed to have been booked in place of the real thing.

Many acres of commentary will doubtless follow on how Chelsea's season may be derailed by this latest Costa crisis – and there is the possibility that some of that may be right.

That, of course, is precisely what Mourinho wants – it deflects attention from his team, and fires up a man who is never better than playing the pantomime villain. Costa will still be one of Chelsea's key men this season – write him off at your peril.

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