PHOENIX -- Zack Greinke's friends warned him against playing basketball but he didn't listen, and now the Brewers' biggest offseason acquisition will begin the season on the disabled list.An MRI scan on Monday revealed the right-hander cracked a rib on his left side when he went up to grab a rebound and fell to the hardwood in a pickup game during the first week of Spring Training. Club officials expect Greinke to miss at least his first two or three starts of a regular season that begins March 31 in Cincinnati. Greinke, a good bet to be Milwaukee's Opening Day starter before he was hurt, made two Cactus League appearances with sore ribs before undergoing the MRI on Monday. It revealed a hairline fracture of his seventh rib and a bone bruise on his eighth rib. The normal recovery time for bone injuries is four to six weeks from the time of injury, Brewers head physician William Raasch said, and Greinke is already about two weeks into the healing process. But Greinke would have to re-establish arm strength once he begins a throwing program, so his rehab will almost certainly extend into April. The Brewers can get by with four starters for all but three dates in April, according to general manager Doug Melvin. Greinke's loss will nevertheless be felt, and he expressed regret about being hurt playing basketball. "I've been doing this for a couple years now, and people are always saying, 'You're going to get hurt,'" Greinke said. "It finally caught up to me. "I was hoping it was just bruised, but I guess it's worse than that. So I guess I have to stop playing [basketball] now. I had a lot of fun while I was doing it, but it wasn't worth it." The Brewers sent four young players to the Royals for Greinke and shortstop Yuniesky Betancourt in mid-December as part of a starting rotation makeover that sparked a run on season tickets and has many of the team's core players talking this spring about making a run in the National League Central. Now they'll have to wait to see Greinke start a regular-season game in a Brewers uniform, if only temporarily. "We're not talking about this gross deformed fracture," said Raasch. "We're talking about something very subtle that we can barely see, and we found it on the MRI. We're not that concerned about it, except the fact that it's bad timing. He's got a sore rib because he fell on it, and unfortunately you stress your ribs when you throw baseballs hard. ... "You have to understand that as it's healing, we're going to progress him and allow him to do more and more things. The ideal situation is that after a week or two [from Tuesday] he'll feel real good, hopefully, and we'll start the throwing program in two weeks and build him up." The injury is so subtle, Raasch said, that X-rays last month did not reveal the fracture. "Let's put it this way: If this was the playoffs, he'd just be throwing with it," Raasch said. "He wants to progress, and our job is to sacrifice a few games now so he can pitch into the postseason." Manager Ron Roenicke delivered the Greinke diagnosis to reporters after the Brewers' 7-1 loss to the Dodgers at Maryvale Baseball Park. He still was not willing to name an Opening Day starter, though right-hander Yovani Gallardo looks like a solid bet to handle that assignment for the second straight season. "We're going to figure things out," Roenicke said. "I haven't named the first start for a reason, because stuff happens. I hate to say something and then all of a sudden I keep changing." The back end of the rotation is the Brewers' more pressing issue, however. With no clear "sixth starter," they will have to find a replacement for Greinke in early April and plan to do so internally, Melvin said. The schedule helps; the Brewers will not need a fifth starter until April 6, and then not again until April 16. The problem is that the leading candidates are behind in their preparation for the season. Left-hander Manny Parra has been bothered by a bad back, right-hander Mark Rogers has yet to appear in a game because of a stiff shoulder and Amaury Rivas, the club's 2009 Minor League pitcher of the year, will miss a few more days because of an infected tooth. Organizational veteran Tim Dillard, who surrendered two home runs Tuesday in two innings against the Dodgers, and prospect Wily Peralta are also candidates to make a start or two if necessary. "Anybody that's in camp, any pitcher that's got a Brewers uniform on and steps up and pitches well could be that guy," Melvin said. "It doesn't mean you replace Zack. It's tough to replace him." Injuries are "part of what we go through," Melvin said. "GMs always live in fear of injuries," Melvin said. "But we think he'll get his treatment and he won't miss a lot of time." As for the off-field manner in which Greinke was hurt, Melvin said, "he told us that day. There's nothing you can do about it. It doesn't matter how he hurt it." What matters is that he heals. "It's not good at all, but on the bright side, hopefully it won't be too long and I won't miss hardly any time," Greinke said. "I just don't want to be away from the team, especially at the beginning."