Defending champions Chelsea's season could be in trouble if striker Diego Costa is unavailable for long, former Tottenham Hotspur manager Harry Redknapp said.

Spain striker Costa, who injured his hamstring during the pre-season and missed Chelsea's Community Shield loss to Arsenal, is a doubt for Saturday's Premier League opener against Swansea City.

"If Costa is injured a lot and is going to be missing, that's the scary part -- can they (Chelsea) get away without him?" Redknapp, who quit as Queens Park Rangers manager in February, said on his official Twitter handle on Tuesday.

"If Costa does pick up injuries, and it seems his hamstring isn't great at the moment, one of (Loic) Remy and (Radamel) Falcao has got to carry the baton and do the job and whether they can is the question mark."

The 68-year-old Redknapp resigned from QPR in February with the club second bottom of the Premier League. They were relegated at the end of the season.

"Maybe Falcao can do the job, Jose's placed his faith in him. Jose (Mourhino) can lift people and improve people and if he can get the best out of him maybe they'll be ok," Redknapp added.