"It's not progressing the way I want it to or the way the team wants it to," Hammel said, "but it's slowly getting better."
Hammel had the knee drained on Monday and the team is doing regular treatment to try to control the fluid buildup.
The righty was given eight days' rest to heal between his May 5 and May 14 starts, but the soreness has lingered.
Hammel said he hasn't run on ground for three weeks, instead opting for the elliptical stair stepper and pool work with a "zero-gravity outfit" that allows him to work on his range of motion while negating impact and potential swelling.
"It's kind of a touchy situation," Hammel said. "I don't know how long it's going to be around, but it's probably something we're going to deal with for a while."
The results of the injury have shown in Hammel's performance. After jumping out to a 4-1 record and 2.09 ERA, Hammel has failed to advance past the first out of the sixth inning in each of his past two starts. He's also given up a combined eight earned runs, raising his ERA from 2.09 to 3.12.
"Obviously I want to be getting deeper into ballgames, but the knee is just not cooperating right now," Hammel said.
While manager Buck Showalter wouldn't say he's confident that Hammel's knee won't be an ongoing issue, he said he felt the situation was manageable.
Very little consideration was given to pushing Hammel's start back further than Thursday, especially given the flexibility the team has with off-days coming up on May 31 and June 4.
"I really feel like just getting me out there every fifth day is going to help the team," Hammel said. "Obviously I don't want to kill the 'pen, but I think missing me for a couple of weeks right now is probably not in the best interest of myself or the team. I know I can help the team right now with this, it's something I can put up with, and I'm just going to keep grinding it out."