The forward joined Bayern Munich on a free transfer from Signal Iduna Park this summer but he pointed out his former side's constant capacity to adapt to major lossesBayern Munich new-boy Robert Lewandowski stressed it would be "dangerous" to think that Borussia Dortmund are no longer a title threat without him starring in attack for them this season.
The striker left Signal Iduna Park on a free transfer for the Bundesliga champions this summer, four years after joining Dortmund, in a move which had been on the cards for over a year and was sealed in January.
Jurgen Klopp's men have lost one of their star players for four successive summers now - Nuri Sahin to Real Madrid in 2011, Shinji Kagawa to Manchester United in 2012, and Mario Gotze and Lewandowski to the Bavarians in 2013 and 2014 respectively.
And Lewandowski has no doubt that BVB will be a threat to Pep Guardiola's charges in the Bundesliga title race regardless of losing him to their main rivals for the championship.
"Dortmund are always dangerous," the forward, 25, told Sport Bild. "They have often shown that they can come back from losses, like with Sahin, Kagawa and Gotze.
"To write them off before the season would be very dangerous. They are a serious competitor for us. We need the rivalry, it's part of football and the competition helps to spur you on and become even better.
"We need to have BVB troubling us to thrive."
Lewandowski is expected to make his competitive debut for Bayern when they face Dortmund in the DFL-Supercup on August 13.
The striker believes that the five months he continued to play for the Ruhr club in 2013-14, despite having signed a deal to leave, made him a stronger footballer mentally.
"I knew that I wanted to give everything until my last day with BVB," he continued. "I learned a lot. The experience made me stronger, especially psychologically.
"It was not easy to hide my excitement at joining Bayern, but I still brought my best performances on the pitch.
"Now I'm at Bayern, I want to win as many titles as possible - all of them, ideally."