But, things could be a lot worse (just ask Cardinals fans). The fracture is minor and he's not expected to miss more than a couple of starts. If this injury occurred in September or October he would pitch through the pain. Additionally, the Brewers' April schedule means they'll only need a fifth starter for 2-3 games all month. Unfortunately the Brewers don't have much depth in starting pitching.
Mark Rogers and Manny Parra seem the most obvious choices to start a couple of games, but Rogers' spring has been slowed by shoulder stiffness (he's had two shoulder surgeries), and Parra has been dealing with back stiffness. Neither will be ready to start for the Crew in April.
So it seems the Brewers might look to a couple of their minor league up-and-comers to step up sooner than expected. The most logical choices are Amaury Rivas and Wily Peralta.
The Brewers intend to give Greinke the time he needs to heal. That should ensure this problem doesn't linger deeper into the season. Greinke starting 29-30 games this year is not much worse than 32-33.