Add featherweight champion Jose Aldo to the expanding list of high profile fighters who recently have withdrawn from UFC events because of injury.
The promotion announced Saturday night that Aldo fell victim to an undisclosed injury and will not defend his title July 21 against Erik Koch at UFC 149 in Calgary, Alberta.
Aldo (21-1) was slated to make the sixth defense of his 145-pound title, which he claimed from Mike Brown on Nov. 18, 2009.
In his most recent outing, Jan. 14 at UFC 142, Aldo knocked out top contender Chad Mendes in the first round.
UFC has not yet determined whether to keep Koch (13-1) on the card, which will be held at Scotiabank Saddledome.
A four-fight win streak put Koch in position to land the featherweight title shot. He is ranked sixth by ESPN.com among 145-pound fighters.
Faber (26-5) originally was scheduled to face 135-pound champion Dominick Cruz on the July 21 card, but a torn ACL -- suffered in March while training -- forced Cruz to pull out of the fight.
Barao (28-1, with one no contest) is the third-rated bantamweight. He has won all five of his fights under the Zuffa, LLC banner.
In addition to Aldo and Cruz, middleweight contender Brian Stann, middleweight contender Vitor Belfort, middleweight contender Michael Bisping, welterweight contender Jon Fitch, former top welterweight contender Thiago Alves and light heavyweight contender Thiago Silva have each suffered fight-cancelling injuries in the past month.