Burnes exited Thursday's start against the Cardinals with lower-back discomfort, Adam McCalvy of MLB.com reports.
Burnes initially talked his way into staying in the game after a visit from trainers, but he was ultimately removed with two outs in the fourth. Initial reports indicated the right-hander was displaying discomfort with his pitching hand, but it now appears that his back was the issue. According to Tom Haudricourt of the Milwaukee Journal Sentinel, manager Craig Counsell said the club would have a better idea of Burnes' status Friday. Should the Brewers qualify for the postseason, they will certainly hope Burnes can pitch one of their games in the wild-card round.