Brown had been pursuing a fly ball from Mets shortstop Ruben Tejada when it happened. The ball dropped, but Brown could not stop his momentum toward the wall. He flipped over the wall and appeared to hit the concrete floor in the seating area hard, although instant replay did not have a good look at it.
Brown eventually got up, but not before Tejada circled the bases for a two-run, inside-the-park home run. Brown seemed to be OK after the incident and remained in the game until the bottom of the fourth.
"He said he hit his knee," Phillies interim manager Pete Mackanin said. "That's what the trainer told me. He hit his knee. We asked him numerous times in the dugout, 'How do you feel? Are you OK?' He said, 'Yeah, I'm fine.' He didn't really look dazed or anything like that. The trainer came up to me the next inning and said he's done.
"We don't want to see that happen to anybody. Hopefully, he'll be fine. If I was told he hit his head I would have taken him right out of the game."
Mackanin said he does not expect Brown, who missed time in 2013 with a concussion, to be in Boston this weekend.
"I guess he took that test and didn't score exceptionally well," Mackanin said.
Todd Zolecki is a reporter for MLB.com. Read his Phillies blog The Zo Zone, follow him on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.