Diego Costa has been ruled out of Chelsea's Community Shield clash with Arsenal with a hamstring injury, casting doubt over the start of his Premier League season.

Manager Jose Mourinho has moved to allay fears over his star striker, describing the injury as "discomfort in his hamstring", but intimating that his omission simply represents a cautious move.

Costa's removal from the matchday squad has cast fresh doubt over his fitness however, with Chelsea kicking off their Premier League title defence against Swansea on Saturday.

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Speaking to BT Sport, the Portuguese admitted he was unsure whether the striker would be fit for the curtain-raiser.

"I don't know if Diego Costa will be available for the start of the season," he said.

"He had a little problem after the Barcelona game. After that he was training normally and we thought he would be ready, but this morning he was feeling uncomfortable."

The Spain international has a long history of hamstring problems, having played for just nine minutes from the start of the 2014 Champions League final for Atletico Madrid while visibly carrying an injury.

Despite scoring 21 goals in his debut campaign in England, Costa missed large portions of the season with a similar injury.

Mourinho told reporters on Friday that "there are no concerns, no protections" for his star striker, but the 26-year-old will play no part in Sunday's Wembley showpiece, with Loic Remy favoured to Radamel Falcao for the lone forward role.

After signing a new long-term deal earlier in the week, Theo Walcott has been handed a starting role by Arsene Wenger, with Olivier Giroud named on the bench.