Radek Stepanek has been ruled out of Wimbledon and the Czech Republic's Davis Cup quarter-final against Chile next month because of a left knee injury.
"His health problems are more serious than he expected," Czech Davis Cup captain Jaroslav Navratil said.
World number 25 Stepanek was seeded 22nd for Wimbledon, which begins on Monday.
Stepanek picked up the injury in Prague earlier this week while he was preparing for Wimbledon, Czech Davis Cup team spokesman Karel Tejkal said.
Stepanek announced in March that he was suffering from a fatigue syndrome and needed at least two months' rest. He returned to action at a challenger tournament in Prostejov earlier this month.
But he pulled out of last week's Gerry Weber Open, the grass-court tournament in Halle, Germany, because of throat inflammation.
Stepanek made a good start to the season by reaching the final of the Brisbane International in January but lost in the first round of the Australian Open and failed to get beyond the second round in any other tournament this year.
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