Rafael Nadal refused to confirm his involvement in the remainder of the 2016 season after he was convincingly eliminated from the Shanghai Masters by Viktor Troicki on Wednesday.
The former world number one came out worst from an attritional contest with the Serbian, who picked up his first career win over the Spaniard 6-3 7-6 (7-3).
Though yet to have officially qualified for the ATP World Tour Finals, Nadal is a shoo-in to earn a spot at the London showpiece.
However, Nadal suggested he had doubts over his ability to take part at the O2 Arena, as he continues to battle back from the wrist injury that wrecked his French Open and Wimbledon.
Nadal said: "I don't know what's going to happen in the next couple of weeks. It something that I need to think about and let's see.
"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.
"I need to speak with my team. I need to speak with my uncle [and coach Toni] too and prepare myself for the calendar to try to do the things that I need to do and to work on things I need to work on, because sometimes to keep competing is not the solution.
"Sometimes the solution is practice and stop and have a process of training. Maybe that's an opportunity to do it. I'm not sure about that.
"I know what I have to do and I am going to do it. I have two months and a half until the next season starts, so I have two months and a half to put myself at the level that I need to be and I have the confidence that I am going to do it.
"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.
"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."