He admits he would have been tempted by a move to the Premier League.
"I don't think you would find any player in the Bundesliga who would say that they would not at all be interested," the forward told Kicker magazine.
"Chelsea would have been very interesting for me. You don't get a chance like that very often in your life.
"(Director of sport) Rudi Voller has explained the reasoning to me several times.
"They could not find a suitable replacement and I am too important to Bayer."