Bayer Leverkusen midfielder Michael Ballack has said that he is shocked by the decline in form of his former team Chelsea.

The 35-year-old, who left Chelsea 18 months ago, was part of the team that defeated the Blues 2-1 in their Champions League Group E clash on Wednesday.

"I knew before the game that Chelsea were going through a difficult moment, but it was only when we were on the pitch that I could understand what was really happening. We could sense in every minute of the match that they were not as strong as they usually are," Ballack said.

"Even when they were 1-0 up we felt they didn't have the mental strength they normally have. We might have been lucky to score our winning goal in the last minute but we always believed we had a chance of doing that.

"I am really surprised at what is happening at Chelsea and, even though it was a big victory for us, I'm not as happy as I would normally be because it was against many of my friends."

The German international spent four years at Stamford Bridge and played under five different managers.

"I know how quickly it can go against them at Chelsea," he added. "It is always difficult for any coach there but Villas-Boas had success at his last team, he is an ambitious young boss and I know he is a good guy.

"At the moment it is not easy for Chelsea but it's not just about the coach. It's also about the players. They are the ones who have to get out of this situation."

Chelsea's Champions League fate will be decided when they face Valencia on Tuesday, December 6.