Seattle Sounders striker Clint Dempsey will miss the remainder of the Major League Soccer season with an irregular heartbeat, the club announced on Tuesday.
The news also likely rules Dempsey out of two United States World Cup qualifiers in November.
Dempsey, 33, has not played since the health issue was diagnosed late last month.
"His return to play is not important relative to his health, both short term and long term," said Seattle general manager Garth Lagerwey.
"We feel that by ruling him out today, it puts us in the best position to eventually get him back hopefully for the 2017 season."
The former Fulham and Tottenham Hotspur player is the all-time second-highest scorer for the U.S. national team, with 52 goals in 130 matches.
Between 2007 and 2012, Dempsey played for Premier League team Fulham and is the club's highest Premier League goalscorer of all time.
Dempsey's absence comes as the U.S. eye the start of the CONCACAF Hexagonal, in which Mexico, Costa Rica, Panama, Honduras and Trinidad and Tobago will also battle for three automatic spots at the 2018 World Cup in Russia.
The U.S. play arch rivals Mexico in Columbus, Ohio on Nov. 11, before facing Costa Rica away four days later.