Marcum pitched three innings against the Dodgers in his Cactus League debut on Sunday. The right-hander is expected to throw 60 pitches in a Minor League his next time out, putting him on pace to be on the bubble as far as arm stamina by Opening Day, when a starting pitcher is ideally good for at least 75 pitches or five innings, but preferably more.
"If we think Marcum is ready, we will not be stretching Marco," manager Ron Roenicke said on Tuesday. "He's already to the point where his next outing he can be at 90 pitches. He's stretched out."
Estrada is 2-2 in six games this spring and has posted a 4.50 ERA in 15 innings. If Marcum starts the season in the rotation, Estrada will be prepared for spot starts should the need arise, with the Brewers confident he'd be able to give them four innings to get through a game.
"When he gets in a starting mode he mixes up locations really well," Roenicke said. "He's pitched better for us as a starter than he has as a reliever, though I like him as a reliever.
"We want him to get back in a mode where we're going to use him two, three innings, maybe one inning. He needs to pitch more often to try and get ready for our bullpen."
The Brewers are keeping their options open by starting Marcum in a Triple-A game Sunday, enabling them to backdate his appearance on the disabled list if they decide he needs more time before joining the rotation.
"Shaun was fine, he understands," Roenicke said, noting that no red flags have gone up regarding Marcum. "In case we want to give him an extra start [in the Minors once the season starts], we can do it."