A deal was struck last month which will see Podolski move to London this summer.
"I have made this decision not against FC Cologne but for this great opportunity and the good of my own individual development," he said.
"This was not an easy decision for me at all, as FC Cologne, our fans and the city are something special for me. I will always carry FC Cologne in my heart.
"We need to pool our strengths now and have to be fully focussed on our survival in the Bundesliga."