Clint Dempsey's Major League Soccer season is finished, and his availability for United States' upcoming World Cup qualifiers is in doubt because of an irregular heartbeat.

Dempsey's club the Seattle Sounders announced in August that the forward was "undergoing medical evaluations" for the problem, and confirmed he had an undisclosed surgical procedure in early September.

There was initial optimism that he would return in the current MLS season, but the 33-year-old stopped training with the club last week.

Sounders general manager Garth Lagerwey announced on Tuesday that his star forward will not play again in 2016.

And worryingly for national team coach Jurgen Klinsmann Dempsey's condition puts his status for the first two games of the CONCACAF qualifiers in jeopardy.

United States host Mexico on November 11 and travel to Costa Rica four days later but Dempsey - who has 52 international goals - is unlikely to be part of the squad..