In a statement released on Monday, UFC officials announced the title bout has been rescheduled for a UFC 175 pay-per-view event on July 5 in Las Vegas.
"Weidman suffered a knee injury that will require minor surgery and his bout with Machida has been rescheduled for Saturday, July 5," the statement read.
The UFC did not announce a new headliner for the May 24 card. Weidman would not comment on the injury.
Weidman (11-0) won the middleweight title in July, when he knocked out Anderson Silva in the second round at UFC 162. He became the first fighter in the promotion's history to beat Silva, ending the Brazilian's 16-0 run inside the Octagon.
He recorded his first title defense in December in an immediate rematch with Silva at UFC 168. The fight ended in the second round when Silva broke multiple bones in his left leg after Weidman checked a kick.
Machida (21-4) is 2-0 since dropping to the UFC's middleweight division last year. A former light heavyweight champion, Machida is 5-1 overall in his last six fights. He's coming off a one-sided unanimous decision over Gegard Mousasi in February.
Weidman, 29, was originally scheduled to fight Vitor Belfort at UFC 173 on May 24, but Belfort was pulled from the card when the Nevada State Athletic Commission banned testosterone replacement therapy last month.
Belfort (24-10) had been approved to use TRT in three consecutive fights in 2013, all of which he won via knockout. The UFC had concerns on whether the Brazilian would be licensed in Nevada and decided to replace him on the card.