Alcaraz has no choice but to withdraw after that ankle injury. It was the sensible option after the week he had.
With that said, I still think his schedule was too much after the US Open. Ideally would have been to play Shanghai after the US Open but I understand that may have been a long break so he should have sticked to playing LC and then Shanghai. But now after playing so much tennis, he’s forced to withdraw from another Masters, his 3rd masters withdrawal this season due to precautionary measures.
It happened in Barcelona as well. I think Alcaraz needs to withdraw from some 500s and prioritise masters more.