Keller (wrist) will try to throw a bullpen session Thursday, Rob Biertempfel of The Athletic reports.
The swelling in his wrist reportedly subsided Wednesday, but it sounds like he's not out of the woods just yet. If he is able to throw a bullpen Thursday and it goes well, he could make his scheduled start Sunday. However, if things don't progress as the Pirates hope, James Marvel is on hand to make Sunday's start if necessary.