Lochte, who won two gold medals as well as two silvers and a bronze at the London Olympics last year, suffered a torn knee ligament and a sprained knee ligament in the incident on Sunday in Florida when a teenaged girl ran at him.
Lochte, 29, caught the girl but they fell and the swim star's left knee collided with the kerb. The girl was not injured. "Thanks everyone so much for the love... will be back at it soon," Lochte tweeted Wednesday.
Lochte the reigning world 200m backstroke and individual medley champion, has been training recently in Charlotte, North Carolina, and was set to swim for the US squad at next month's Duel in the Pool in Scotland.
"As a result of a freak injury caused by an unexpected fan encounter, Ryan has suffered a torn MCL and an ACL sprain and will be taking a break from training and competition," a statement from Lochte's publicist said. "His medical team expects him to make a full and speedy recovery."
Lochte has been a member of the 4x200m freestyle relay team which has won gold at the last three Olympics. He won the 200m backstroke title at the 2008 Beijing Olympics and the 400m individual medley gold at the London Games.