Former Chelsea forward Gianfranco Zola has claimed that the poor form of Eden Hazard and Diego Costa has contributed to the club's dismal season so far.

The Blues eased to the Premier League title six months ago, but they are now just three points above the relegation zone after 12 games.

Jose Mourinho's side have lost seven of their league fixtures, and Zola believes that Hazard and Costa are among a number of players who have failed to match last season's form.

"There is one compelling reason for the poor start to the season," Zola told reporters. "The poor form of key offensive players Eden Hazard and Diego Costa has not helped.

"Defensively as well the team has dropped the standards set last year so the players have lost confidence as a group and this has led to poor results. The club has it in them to turn around their fortunes."

Chelsea are now 13 points adrift of fourth place.