The 34-year-old spent four seasons with the Blues before joining Leverkusen last year on a free-transfer.
He will return to Stamford Bridge when his side take on Chelsea in the opening Champions League Group E match on Tuesday night.
Looking ahead, Ballack insists Leverkusen have what it takes to stun his former side.
"We have a bit of international experience thanks to the Europa League last season, but of course it's completely different to be playing in the Champions League," Ballack was quoted as saying on the Uefa website.
"I know from experience that it's a different level. Yet in the opening match in London, where we can go without any pressure, we may spring a surprise."
Ballack is also delighted with the chance to return to Stamford Bridge.
"I was very happy. For me the draw could hardly have been any better. I am looking forward to travelling there again, to playing there. Emotionally this will certainly be a special match for me."
Leverkusen will be high on confidence ahead of Tuesday's match following their 4-1 Bundesliga win over Augsburg at the weekend.