Centurion Ballack: Chelsea more dangerous
"This is something special," the former Germany skipper told reporters on the eve of the match. "The number 100 means quite a bit."
The Londoners have a two-point lead over Leverkusen at the top of Group E and Ballack is expecting a reaction after his old team lost 2-1 at home to Liverpool on Sunday, their third defeat in four matches in the Premier League.
"Chelsea know how important this game is and top teams are the ones who deliver under pressure," said the 35-year-old. "This makes Chelsea more dangerous.
"But we can also beat them, we are playing at home after all. It is a fantastic game for us and everyone has been waiting for it."
Ballack rejoined Leverkusen in 2010 for a second spell at the club after spending four years in London and is back in top form.
"We cannot hide and we should not be afraid," he said. "We have won both our home games so far and now we can make it three.
"We did not get into this competition just to take part. We have the quality to advance and we need to get that into our heads."