article_snippet.sent: Costa returns to training with the first-team squad this week, but Chelsea may be reluctant to throw Chelsea in from the start against Arsenal, given how Chelsea broke down with the hamstring problem that has troubled Chelsea for much of the season against Stoke City.
article_snippet.sent: Diego Costa returns to training with the first-team squad this week but may not be thrown in against Arsenal .
highlights_snippet.sent: Costa returns to first-team training this week to boost Jose Mourinho .