The Poland international has attracted the interest of a number of big teams from across Europe as he's available on a free transfer next year.
The 25-year-old recently announced that he would sign a contract with Bayern Munich in January after a move to the German champion fell through during the summer, only to claim shortly after that he had been misunderstood.
His latest comments put clubs such as Barcelona, Arsenal, Chelsea and Manchester United on red alert, but Lewandowski has now made it clear that he has already made up his mind.
"I am feeling very well at Dortmund, but I want a new challenge next season," Lewandowski told Sport Bild. "I can only say one thing about my future and that's that I will announce my decision next year.
"No club has to bother with a fresh approach. I am focused on Dortmund and will not let anything distract me."
Lewandowski has been in fine form so far this season, scoring 13 goals in 17 appearances in all competitions.