LONDON -- The most significant moment of Sunday's Community Shield came not in the match, but in Jose Mourinho's post-match press conference. There was the usual Arsenal-baiting guff -- his first answer was a master class in Jose-speak as he said the media were usually wrong when discussing defensive football; but that, if it were right, then his side had been the better team, a moral conundrum that effectively meant to praise Arsenal was to be hypocritical.

And then came a moment of frustration that hinted at some genuine anxiety for the reigning champions.

Last Friday, Mourinho had said that Diego Costa would play in the Community Shield despite suffering a hamstring injury in the friendly against Barcelona. The striker, though, wasn't even in the squad for the Community Shield.

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"Will Costa be fit for Swansea [Saturday]?" Mourinho asked. "I don't know. You think I'm lying, but I'm not. Two days ago he was ready to play and yesterday he trained normal. The next time you ask me about Costa's fitness, I prefer not to answer. Maybe yes, maybe no."

Costa's hamstrings are perhaps the most important factor in Chelsea's attempt to defend its title. He often played through pain at Atletico Madrid in 2013-14 before breaking down in the Champions League final. Last season, his hamstrings were a constant issue: even though he played with the problem in a number of games, Costa was unavailable for 73 days because of the weakness.

Perhaps both player and manager would be more willing to take a risk for a league game than for what is essentially a glorified friendly, but the impression remains that Costa cannot be relied upon to play every week.

That in turn places pressure on Costa's back-ups. On Sunday, they were found lacking. Although Loic Remy scored nine goals in all competitions last season, he has never seemed a natural fit for Chelsea's tactical approach.

At Queens Park Rangers, Harry Redknapp quickly decided Remy could only play in a front two because he lacks the physical presence to hold the ball up. Jose Pekerman, the Colombia coach, reached a similar conclusion about Radamel Falcao, who replaced Remy at half-time. Neither impressed playing as a lone striker, and the result was that Chelsea looked toothless.

Losing the Community Shield isn't a disaster, and the impression was that Arsenal are further along in their fitness work for the new season than Chelsea, which are perhaps looking to peak later to try to avoid the fatigue that so afflicted them in the spring last season.

Although Chelsea won the title comfortably enough, there were some weary performances in March and April -- most significantly in their Champions League exit against Paris St-Germain -- and that might have proved more of a concern if any of Chelsea's rivals had mounted a concerted challenge.

Mourinho is unusual in the modern game in eschewing rotation to work with a tight-knit core, but given how exhausted Nemanja Matic and Cesc Fabregas looked in last season's run-in, it's a surprise there hasn't been a move for another midfielder to ease the burden on them.

Perhaps the plan is for Ramires, who started the Community Shield, to play a more active role this season -- and there is still, of course, John Obi Mikel.

The other issue is the ongoing dance on the right side of midfield, where Victor Moses is back from two seasons on loan at Liverpool and Stoke City. Juan Cuadrado will be looking to avoid being another Kevin de Bruyne, Andre Schurrle or Mohamed Salah, players Chelsea bought and swiftly offloaded. Willian remains the player to dislodge.

In terms of the first XI, Chelsea were by some margin the best side in the league last season and there's little reason to suppose that will be any different this season, particularly given that they are far more equipped to play defensive football than any of their rivals, Arsenal's new-found pragmatism notwithstanding.

Yet Chelsea's squad also seems to lack depth both at center-forward and in midfield. In that regard, Chelsea's lack of transfer activity has been a little puzzling.

A deal for Ghana left-back Baba Rahman, to replace Filipe Luis who has returned to Atletico Madrid, is almost complete, while there have been two bids for Everton central defender John Stones; otherwise the only signings have been Asmir Begovic, bought to replace Petr Cech as back-up for Thibaut Courtois, and the now-familiar raft of teenagers.

Mourinho combusted in his third season at Chelsea last time and in his third season at Real Madrid. He seems a mellower figure these days, but it's not hard to imagine the lack of investment being the spark that ignites another blaze.