Rafael Nadal absorbed a 6-3 7-6 (7-3) body blow from Viktor Troicki to exit the Shanghai Masters, with the loss leaving the struggling Spaniard unsure of the remainder of his season.
The 2009 finalist will drop out of the ATP top five as a result of his second-round loss to the Serb.
He is already qualified for the November World Tour Finals, featuring the top eight players on the ATP - but may now not front up for the London showpiece.
Australia's world No.14 Nick Kyrgios is ranked 12th in the race to the World Tour Finals and would potentially benefit from Nadal's withdrawal, though the volatile star said he "couldn't care less (about qualifying), to be completely honest with you" after a meek loss to Russian journeyman Mischa Zverev.
Nadal now fears that he may have to cut his losses by ending his season early and concentrating on what is missing from his once imperial game.
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"For me the season is almost over and I accept that. Just looking about what I need to do to be 100 per cent ready for the beginning of the next season," the 30-year-old said.
"That's my motivation, that's my goal. I am going to do all the things that I need to do to make that happen."
But he warned that he might have to take drastic measures to shore up his fading form: "I don't know what's going to happen in the next couple of weeks. I cannot say now what I am going to do during the next month.
"I'm not sure about my calendar. I'm not sure about the things that I need to do to try to be at 100 per cent ready for the next year."
