Hideki Matsuyama and Will Zalatoris withdrew from the WGC-Dell Technologies Match Play event before their Friday tee times.
Matsuyama is dealing with a neck injury and Zalatoris has an illness, according PGA Tour officials.
By conceding the match, Matsuyama's scheduled opponent Max Homa received the day off and a spot in the knockout stage of the competition in Austin, Texas.
Matsuyama, 31, reportedly spent about 20 minutes on the range at Austin Country Club, trying to loosen up before making his decision.
The 2021 Masters champion's withdrawal also knocked out fellow Group 5 member Justin Suh. Suh needed to win his match on Friday against Kevin Kisner and have Matsuyama defeat Homa to force a playoff to decide the group winner.
Matsuyama defeated Kisner 1-up on Wednesday and lost 3 and 1 to Suh on Thursday.
Zalatoris, who was runner-up to Matsuyama at the 2021 Masters, conceded his Group 7 match against Ryan Fox.
Zalatoris, 26, lost 3 and 2 to Andrew Putnam on Wednesday and lost 5 and 3 to Harris English on Thursday.
--Field Level Media