Marcum, 30, is still slated to join the Brewers for the season-opener but has been battling shoulder soreness and was scratched from his scheduled Cactus League start on Saturday.
"He's going to get up on the mound today, throw a little bullpen and we'll see how he comes out of that," Roenicke said Tuesday morning. "And if that's good, just catch, and another bullpen the next day. He's coming along pretty good."
Marcum, who missed the 2009 season to recover from Tommy John surgery, has logged at least 195 innings each of the last two seasons -- the most recent for the Brewers, when he won 13 games.
Roenicke said "if everything went perfect" that Marcum would still be on pace join the Brewers on Opening Day, but would be on a restricted pitch count.
"But if you remember last year, he was so efficient with his pitches," Roenicke said. "He would throw his 80 pitches and could be in the sixth inning, easily."