Injury-hit Japan No 1 Kei Nishikori said on Thursday he had failed to recover from an elbow injury and will sit out the behind-closed-doors Davis Cup qualifier against Ecuador at the weekend.
A depleted Japan will also be without world No 48 Yoshihito Nishioka when they bid to reach the finals in Spain later this year.
Nishioka has opted to return to the United States as a precaution against being quarantined because of the novel coronavirus outbreak ahead of next week's ATP Tour Masters event in Indian Wells.
President Donald Trump has suggested that the US might consider imposing restrictions on people travelling from Japan because of the virus threat.
No fans will be present when the Davis Cup tie begins on Friday to reduce the risk of infection as a growing number of sporting events across the globe are affected by the outbreak.
World No 31 Nishikori said he was still not fit enough because of the nagging injury, which required surgery in October, and he gave no definite timeline for his return to action.
A former Grand Slam finalist, Nishikori has not played competitive tennis since losing in the third round of the US Open last August.
He was seen practising his serves this week but told a press conference on Thursday: "Physically I'm not at my max.
"I want to return to competition after I improve my strength and become fully confident.
"It might be after Miami or during the clay season," he added, referring to the Miami Open which begins on March 25.
The draw for Friday's singles sees 117th-ranked Go Soeda for Japan play Emilio Gomez (ranked 151), while Yasutaka Uchiyama (90) will face Roberto Quiroz (276).
On Saturday, the doubles pits Ben McLachlan and Yasutaka Uchiyama against Gonzalo Escobar and Diego Hidalgo before the reverse singles to decide who will progress to November's 16-team finals in Madrid.