Indians first baseman/designated hitter Jason Giambi has been diagnosed with a small non-displaced rib fracture on his right side and will be out three to four weeks, the Tribe announced Thursday.

Giambi was hurt when he was hit by an Edwin Jackson pitch in the third inning Friday against the Chicago Cubs in Mesa. Giambi experienced increasing discomfort since and underwent an MRI Wednesday. Manager Terry Francona said the Tribe's initial X-ray didn't show anything. Giambi said he also had an ultrasound.

"What we do is treat the symptoms. He's going to be down for a number of days without activity and just getting treatment," Francona said. "When the symptoms are better, we can start getting him into activities, then we can start getting him into baseball activities."

Giambi had he had an inkling when he was hit that it might be serious. He said it was the first time in his career he's had a rib injury.

"It was cutter in and it kind of got me underneath the pad," Giambi said. "I usually can get my elbow pad down, I just didn't get it down in time. I was at first base going, 'Oh, this doesn't feel....'"

Giambi picked the ball up and flipped it to Jackson.

"I wasn't going to let him know it hurt," Giambi said.

"I think I'm l like 10th all-time getting hit by a pitch and I knew this one was different. I came in the next day and told the trainers, 'This one's sore.' I’ve been hit a gazillion times and I just kind of knew this one was different."

The injury could open the door for players on the bubble like outfielders Nyjer Morgan and Jeff Francoeur and infielder Elliot Johnson to make the 25-man roster going into Opening Day March 31 at Oakland.