Cubs pitcher Mark Prior struggled to get out of the second inning of his rehab appearance Monday for Chicago's Class A affiliate, the Peoria Chiefs. The 25-year-old right-hander threw 44 pitches in two innings, giving up four hits and three runs. He's been on the disabled list all season as he works his way back from a sore shoulder. "You can only do so much," Prior said. "I've been doing everything I possibly can every day and I just have to let nature take its course."