Jackson, left fielder Alfonso Soriano and shortstop Starlin Castro converged on a fly ball in shallow left-center field with one out in Friday's game. Jackson ran into Soriano and fell to the ground -- as did the ball -- and remained there for several moments before getting up and finishing the inning.
Cubs manager Dale Sveum said the rookie is fine and probably would be available for Saturday's game.
"It's kind of basically like he got hit by a truck or something, more than anything," Sveum said. "Kind of a whiplash-type effect."
Jackson, the clubs' first-round pick in the 2009 First-Year Player Draft, has struggled since being called up from Triple-A Iowa on Aug. 5. The 24-year-old entered play Saturday with only two hits in 17 at-bats (.118), and had struck out 11 times.
Vice president of scouting and player development Jason McLeod said part of the reason the organization decided to have Jackson -- who has always struggled with strikeouts -- join the Cubs now was so that he could get a fresh look. The chance for Jackson to work directly with Sveum and hitting coach James Rowson also was a positive, and McLeod said he thinks the promotion will be good for the youngster.
"Brett knows he has things to work on, and he's got the character and makeup to work on those things," McLeod said.