Hamels, the Phillies opening day starter in 2013, entered camp behind schedule after dealing with biceps tendinitis that began in November. Hamels said he was healthy upon arriving at camp last month.
But after throwing off the mound Saturday for the third time this spring, Hamels said he no longer feels so good.
"I believe I threw 35 pitches," Hamels said Thursday. "To my body, it felt like a thousand."
Hamels was scheduled to face hitters for the first time in a live bullpen session on Thursday. That's been postponed and he won't throw off the mound again until sometime next week at the earliest.
When asked if he still believed he could join the Phillies rotation in April, Hamels was non-committal.
"I think that's the last thing I'm going to think about," he said. "Ultimately, I just want to get back out and get on the mound and see how I'm going to fare there."
No MRI is schedule for his fatigued left arm, he said. The 30-year-old Hamels went 8-14 with a 3.60 ERA in 33 starts last season.
A three-time All-Star and former World Series MVP, Hamels is entering the second season of a six-year, $144 million contract, the largest contract in Phillies' history.