The truth about how important Costa is for Chelsea
Costa's 20 goals in 26 league appearances were crucial as Jose Mourinho's side took an early grip on last season's title race that they never relinquished.
But concerns about the Spain striker's fitness became a recurring theme throughout the campaign and it frequently took the brilliance of Eden Hazard to make up for the side's diminished attacking threat whenever Costa was absent.
And the sight of Costa limping out of a recent friendly with Barcelona followed by his enforced absence from last weekend's Community Shield prompted fresh concerns that the former Atletico Madrid star's problems have not yet gone away.
Chelsea manager Mourinho has stuck by his policy of operating with a squad that includes just three strikers, with Radamel Falcao arriving on loan from Monaco to join Loic Remy as back-up to Costa after Didier Drogba moved to Major League Soccer's Montreal Impact.
The evidence of pre-season, however, has been that Chelsea's attacking options appear under-powered compared to their main rivals and while Mourinho has not ruled out the possibility of Costa facing Swansea when the champions return to action at Stamford Bridge, the chances appear slim.
Mourinho's team have failed to win any of their warm-up games in 90 minutes and meet Swansea after suffering successive 1-0 defeats, first to Arsenal at Wembley on Sunday and then at home to Fiorentina on Wednesday.
And while the usual caveats about friendly matches apply, Chelsea have looked alarmingly blunt in front of goal, with Falcao -- who endured a miserable loan spell at Manchester United last season -- showing few signs of returning to his best.
- Unique challenges -
Falcao netted only four goals in 29 appearances for United and he acknowledges it isn't easy to adapt to the unique challenges of the Premier League.
"It's a lot more physical here than anywhere else in Europe," Falcao told Chelsea's website.
"It's a very, very competitive league where each team gives absolutely everything they've got in every game they play.
"It demands 100 per cent of your ability and focus because it is very competitive, very physical and tactical too.
"Maybe the football philosophy is a little different here in that it is always about getting the ball forward and there is less time when teams are just trying to control the ball and take the heat out of the game."
Other than Falcao, Asmir Begovic is the only other new arrival, brought in from Stoke to replace departed goalkeeper Petr Cech, although Mourinho is keen to bring in a left-back as back-up for Cesar Azpilicueta.
The Blues boss doesn't get many things wrong, but if Chelsea's title defence falters, he will find himself accused of failing to build on a side that won the title at a canter.
The likely absence of Costa would provide Garry Monk's Swansea with a welcome boost ahead of one of their most testing fixtures of the season.
And Swansea captain Ashley Williams said: "At the moment I think the most difficult Premier League striker to play against is Diego Costa, he scored a few goals against us last season.
"He's one you don't look forward to playing against to be honest.
"It seems he might miss Saturday's game, but you never really know until you get to the ground and look at the team-sheet.
"Whatever eleven they field is world class so it doesn't matter too much, but obviously if he didn't play it would be a bonus for us."
Swansea are hoping to build on last season's success of finishing eighth in Monk's first full year in charge and the arrival of Andre Ayew from Marseille should provide an additional attacking threat this year.