Olympic triathlon champion Alistair Brownlee will have ankle surgery on Wednesday, ruling him out of next month's World Series grand final.
Brownlee aggravated a long-standing ankle problem at August 2's Olympic test event in Rio de Janeiro and his absence in Chicago on September 19 will hold up his qualification bid for next summer's Games.
British Triathlon performance director Brendan Purcell told BBC Sport: "There has been a fairly lengthy consultation to consider all of the options, and Alistair has been fully involved in this.
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"Finishing this season was initially a priority, but given all of the advice offered by the medical teams, having the surgery now was the preferred option.
"We all wish Alistair well and want to see him back fit, healthy and ready to go again."
Brownlee, 27, won the gold medal at London 2012 with his younger brother Jonny taking bronze. Jonny Brownlee is currently out of action with a stress fracture to his left thigh, making him a major doubt for the Chicago showpiece.
The Yorkshire siblings will still have the chance to earn their places at Rio 2016 in a selection race in the new year.