Ishikawa, who had been sidelined since May 27 with a left oblique strain, said he is near 100 percent after six games with Triple-A Nashville.
"I was just counting down the days to be back," Ishikawa said. "I was feeling pretty good down there and seeing a couple games on TV made me want to get back that much quicker."
Ishikawa said he didn't have any setbacks and was able to play without any hesitation or apprehension, even while swinging, which he said is the hardest part when returning from an oblique injury.
"You can feel a little bit of tightness there with certain swings," he said. "Everybody I've talked to that's had this injury said you're going to feel a little bit of tightness. But it's not the grabbing, it's not the sharp pain I was feeling before. I played a week's worth of games down there with 100 percent intensity."
Brewers manager Ron Roenicke said he's not sure what the exact plan is yet for Marcum, though he expects the starter to return June 30 or July 1, having him miss just two starts since the injury.
"The feeling was we would have to push him to that start, and we didn't know if we wanted to do that," Roenicke said.