Happ was scratched from the lineup for Sunday's game against the Marlins due to left knee discomfort, Vinnie Duber of the Chicago Sun-Times reports.
It's unclear when exactly the injury surfaced for Happ, who started the past four games and went 2-for-4 with a walk and two RBI in Saturday's contest. Tyrone Taylor will instead start in left field in the series finale at Miami.