Defending champions Croatia will be without Marin Cilic in the Davis Cup finals later this month after the former US Open winner announced his withdrawal on Thursday because of a knee injury.
Croatia, who beat previous winners France in last year's final, play the inaugural match in Madrid against Russia on November 18.
"My recurring knee injury has continued to give me problems, and as the season progressed it was becoming more evident that surgery was inevitable," Cilic, world number 39, wrote on Facebook.
The "rehab work was successful enough that surgery is not necessary at this stage," he continued.
"However, I will need to undergo a few minor interventions which will keep me off the tennis court for a longer period and unfortunately means I will not be able to compete at the Davis Cup this month."
Adding that he was "extremely disappointed", the 31-year-old Croatian said he would dedicate himself to getting back into shape to kick off the 2020 season "healthier, more prepared, and more motivated than ever".
Cilic was supposed to play in a squad of five Croatian players which includes Borna Coric, Mate Pavic, Ivan Dodig and Nikola Mektic.
According to the Sportske Novosti daily paper, he will be replaced by veteran Ivo Karlovic, 40.
Davis Cup's new 18-team format has replaced the former World Group.
The nations have been split into six three-team groups, with the winners and two best runners-up advancing to the quarter-finals.
Russia and Croatia have been drawn alongside Spain in Group B.
Marin Cilic has withdrawn from Croatia's Davis Cup squad becuse of a knee injury