Alaba has confirmed that he'll leave the Bavarian club at the end of the season, but despite speculation linking him to Real Madrid, he hasn't yet revealed where he will play next term.
"It won't be a step back for him," Kohler said. "Despite Bayern being one of the three best clubs in Europe.
"He's taking this next step mainly for money, and I can understand that. He's 28 and will sign a four- or five-year contract.
"Money plays an important role. You can't blame him. It's perfectly legitimate."
Kohler admitted that he himself left Bayern for financial gain when he joined Juventus in 1991.
"I also left for money," he said. "Of course, my move to Italy was very good for me, particularly in terms of personal development.
"But that wasn't my first thought. I know it would be a nice fairytale if I said that it was.
"Footballers only have a few years to play. Serious injuries can happen, too."