The Blues are currently top of the Premier League by six points after winning their last 11 on the bounce.
But Harry Redknapp thinks if Costa gets injured, Antonio Conte will face a massive challenge for the remainder of the campaign.
He told Betsafe: “Chelsea have created a nice gap at the top, and the teams below can’t afford the gap to get any bigger.
“If Diego Costa picks up an injury during the campaign it could change Chelsea’s season”
“Chelsea have a few a suspensions this weekend, including Costa – who will be a huge miss, and if he picks up an injury during the campaign it could change Chelsea’s season.”
Costa is the top scorer in the Premier League with 13 goals in 17 appearances.
But the Spaniard will not play against Bournemouth on Boxing Day as he is suspended after picking up his fifth yellow card at Crystal Palace last weekend.
The Blues will be confident of extending their winning streak and their six point lead over Liverpool going into the clash at Stamford Bridge.
Chelsea have gone on to win the Premier League on the four previous occasions they have been top on Christmas Day.