An MRI performed on Friday afternoon showed that Brown has mild strains in the posterior cruciate ligament and medial collateral ligament of his right knee and will be shut down for seven to 10 days. He will have to wait for the swelling to go down before he resumes baseball activities.
Brown, once regarded as the top prospect in the organization, was hitting .266 with four home runs and 22 RBIs, but he hit all the homers and put together seven multi-hit performances in his last 17 games.
He also missed a handful of games in May with an injury to his left hamstring.
He is not worried about his latest setback.
"I'm just going to miss a couple of days, hopefully," said Brown, who spent parts of 2010 and 2011 with the Phillies. "Injuries are part of the game, and that's it. We've still got a couple of months to go. We'll see what happens. I think I'm in a good spot."
This latest injury occurred in Brown's fourth-inning at-bat on Thursday. After hitting a ground ball to third base, he tweaked his right knee going out of the batter's box and labored down the first-base line. He struggled to get to a ball in the outfield the next inning and exited the game at the start of the sixth.
Brown said that the knee had been nagging him since he made a diving catch on the warning track in center field a couple of weeks ago, but he didn't think it was anything serious. On Friday evening, though, he said it feels like he has a "dead leg."
"But the swelling came, and I can't do anything about that," he said. "Once we get the swelling down in a couple of days, then we'll see where we're at."
Though Brown does not seem concerned, the timing of the injury is not good, as he is in Triple-A to get everyday at-bats and improve his defense in left field.
"It's not good timing for him, and it doesn't help him put together a full year or a half of a year or three-fourths of a year," Lehigh Valley manager Ryne Sandberg said. "He's been slowed up with injuries, and his numbers reflect that, especially his power numbers. But he showed some signs the last couple of weeks of getting ready to get hot, [but] now [there's] one more setback at not a good time for him."
Jake Kaplan is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.