Former Chelsea star Gianfranco Zola believes Eden Hazard and Diego Costa's disappointing performances in the opening months of the 2015-16 campaign are the main reasons behind the Premier League champions' poor run of form.

Hazard was voted the PFA Players' Player of the Year last term, but has been struggling so far this season, while Diego Costa has been far from prolific, netting just twice in 10 league appearances.

Zola, who lit up Stamford Bridge between 1996 and 2003, feels the attacking duo's woes have had a major negative impact on the team.

"There is one compelling reason for the poor start to the season," Zola was quoted as saying by London Evening Standard.

"The poor form of key offensive players Eden Hazard and Diego Costa has not helped."

Zola refused to solely blame the front men though, pointing out the fact that Chelsea have also been unimpressive at the back.

"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," he added.

Nevertheless, the Italian remains optimistic Chelsea will get back on track sooner rather than later.

"The club has it in them to turn around their fortunes."