Originally Posted by smoledman
He put it on during the Tomic match as well, whenever the temperature gets below 70F. It's precautionary, it doesn't mean he's suffering back pain. In fact looking at his average 1st serve speed I'd say he's just fine.
If it were precautionary, he would have put on the undershirt before the match, just like players tape their ankles before a match as a precautionary measure. And he would have done it for every match during his career, yet the only other time he has done it was during Wimbledon last year. Besides, the temperature was already in the 60's before the match even started.