Really? it must of been cramps from the cold weather hence why he put the sweater on because i didn't see any time during the match where he could've tweaked it . but he still was moving fine and his ball striking was still not affected .sounds to me like cramps , if that's the case , some good stretching and keeping his back warm will do the trick.
hope you're right and it was just the weather.
do we know what time he's playing tomorrow yet?