New Chelsea manager Antonio Conte has to sign a new defender if the Blues are to challenge for next season's Premier League title, Gianfranco Zola said.
The 49-year-old says his former club will have a "difficult task" in next season's Premier League campaign as there will be a lot of competition.
He added that strengthening the defensive department is a must.
"I think Chelsea will have a difficult task," Zola told talkSPORT.
"There will be a lot of competition; much more than in the past. I know [Antonio] Conte and I know Chelsea, it's a wonderful club.
"But in my opinion, if he wants to play the system that he likes to play at the moment, which is the 3-5-2, then I'm sure he will be looking for defensive positions.
"I'm sure they will be up for it, whether they can win it I don't know because the competition is really strong."