Jackson had some minor cuts to his face after hitting the wire mesh fence near the visitors' bullpen as he grabbed Andrew McCutchen's fly ball to end the sixth inning and strand two baserunners.
The rookie had failed to snare Pedro Alvarez's fly ball at the wall in center in the fifth, resulting in a double and the only hit in six innings off Cubs starter Travis Wood.
"I was [ticked] I missed the first one," Jackson said. "It's almost inexcusable. I've got to catch that ball, and I wasn't going to let another one drop. I was joking with Travis and told him he wasn't going to go nine innings. He said he would've. I was disappointed I didn't catch that first one."
After making the catch, Jackson lay on the ground for a few minutes, and admitted he was "seeing stars." His teammates, Cubs manager Dale Sveum and the athletic trainers ran to him.
"I was very scared, because he hit the fence very hard," Alfonso Soriano said. "Thank God he's OK. I hope in a couple days, he's back."
Jackson was able to walk off under his own power, with a trainer on each side. He was due to lead off the Cubs' seventh but was lifted from the game for pinch-hitter Tony Campana.
The medical staff told Jackson it was a good thing he was in the air when he hit the wall. If his foot had been on the ground, he might have blown his posterior cruciate ligament.
"Whatever my knee hit didn't give," Jackson said of the metal post.
His right knee was bruised and bleeding from the collision. Apparently, Jackson isn't afraid of making contact with inanimate objects.
"I've been fairly lucky with injuries throughout my career," Jackson said. "I've hit walls pretty hard and tweaked stuff here and there, but nothing too serious ever -- knock on wood. It's important to play the outfield without fear, it's important to play the game without fear. That doesn't mean I'm 100 percent fearless."