Chelsea manager Jose Mourinho has revealed that he left Diego Costa out of the starting line-up to face Schalke because he wasn't fit, with persistent issues preventing the Brazilian forward from featuring in three matches a week at this stage.
Costa has been sensational since swapping Atletico Madrid for Stamford Bridge in a £32.5m summer switch, scoring seven times in four Premier League games.
Mourinho decided to give Costa a rest in Chelsea's Champions League opener against Schalke last night and the move backfired, with the Blues quite surprisingly held to a 1-1 draw as Cesc Fabregas had his opener cancelled out by Klass-Jan Huntelaar.
Perhaps a small chink in Chelsea's armour at last
That's the first time Chelsea have failed to win this season and Mourinho quite surprisingly shared in his post-match press conference that he has serious concerns surrounding Costa's fitness, which will force him to ration his minutes in the fight for trophies on two fronts.
The Blues boss told Sky Sports: "Diego Costa is not in condition to play three matches in a week.
"He has problems when he plays one game, he needs a week to recover and now playing matches Tuesday and Wednesday he can't do it. He was not in a condition to do more than he did."
Time to wrap up Costa in cotton wool
Hamstring complaints have been a common theme during the 25-year-old's first two months as a Chelsea player, but on each occasion he's shrugged off niggles to help Chelsea maintain a 100% start to their Premier League campaign.
Mourinho erred on the side of caution for the Schalke game though and picked veteran Didier Drogba to lead the line in attack, although he missed a gilt-edged opportunity that ultimately proved costly.
Costa and fellow summer signing Loic Remy both came on to try and repair the damage with 16 minutes to go, but Schalke rode their luck and just about held firm to take a point back to the Ruhr region.
City showdown looms large
Disappointment over that result in West London will soon subside ahead of preparations for a blockbuster domestic showdown with defending Premier League champions Manchester City at the Etihad on Sunday afternoon.
Mourinho almost certainly decided to leave Costa on the bench with that clash in mind, with little doubt that the feared forward will be raring to go in a mouth-watering showdown between this season's two title favourites.
Long-term though Costa's fitness is definitely a situation Mourinho must keep a very close watch on, part of the reason surely that he made a move to sign Remy with less than 72 hours of the summer transfer window remaining.
One look at Chelsea's problems in attack last season tell you just how crucial keeping Costa fit is to their trophy charge, so don't be surprised if Drogba and Remy are playing plenty in cup competitions to keep their main man ready for the big matches after Mourinho's frank admission.