"Couldn't have surgery today cause I'm sick and running a fever so we are set to try it again next Monday," Harrison wrote.
Harrison's agent, Bill Parise, told the Pittsburgh Post-Gazette earlier Monday that the procedure on his client's lower back will be "very routine."
"They do not anticipate any difficulties," Parise said. "He's going to be fine."
Parise added that Harrison should be able to train again four to six weeks after surgery.
Harrison is coming off another impressive season in which he had 10.5 sacks. He also was fined $100,000 by the NFL for illegal hits this season.
Harrison was chosen the NFL Defensive Player of the Year after the 2008 season, and he capped that campaign with a 100-yard interception return for a touchdown in Super Bowl XLIII.
The Associated Press contributed to this report.