CINCINNATI -- Milwaukee Brewers right-hander Matt Garza, who left his last start after bruising his left thumb while batting, returns to the mound Monday against the Arizona Diamondbacks at Miller Park.

Manager Ron Roenicke doesn't expect the thumb to be an issue, but he is still waiting for Garza to get back to being the pitcher he is accustomed to seeing.

"I've been coaching against him for a long time, even when he was with Tampa," Roenicke said. "He hasn't gotten in that groove yet. First game of the season, fantastic. Since then, it's been up and down."

In his first start, Garza allowed just one run and two hits in eight innings against the Atlanta Braves. He walked one and struck out seven. Garza now leads the Brewers' pitching staff with 12 walks and 20 earned runs allowed in 36 innings. He is 1-3 with a 5.00 ERA in six starts.

Garza, who signed a three-year deal with Milwaukee in January, had a 3.84 ERA in 191 career starts coming into this season. Roenicke is looking for some improvement Monday from Garza, who is 3-1 with a 2.84 ERA in four career starts against Arizona.

"This is a guy that gets after it," Roenicke said. "When he does that, you're going to have a tough time. Whether it's just physically (or) the mental part of being aggressive, he has to get back."