Hayes suffered a left shoulder contusion during Sunday's Double-A game and has yet to resume any game activities, Bill Brink of the Pittsburgh Post-Gazette reports.
Director of sports medicine Todd Tomczyk said Wednesday that Hayes tripped out of the batter's box and hurt the shoulder, and added that the organization is taking it day-to-day at the moment. 107 games with Altoona this year, Hayes has slashed .281/.362/.439 with seven home runs, 38 RBI and nine stolen bases.