Nadal has been battling a right knee injury that saw him pull out of the Paris Masters during the tournament.
The Spaniard had already wrapped up the year-end world No 1 ranking but was desperate to play in London in a competition he has never won.
And despite fears he might pull out of the event at the O2 Arena, he was today spotted hitting freely with his coach ahead of his clash with David Goffin.
Nadal is expected to attempt to play through the injury at the very least, although at Friday’s media day he refused to guarantee the progress of his recovery.
“I’ll try my best,” Nadal said.
“If I didn’t believe I would not be ready for Monday I wouldn’t be here.
“We are working hard and I’m practising well, just trying to be ready for the action.
“I’m going to play. That’s what my feeling is today.
“I can’t predict what might happen in the next couple of days but my feeling is that I’m here to play and to try my best.
“I go day by day. When you have problems with physical issues you cannot predict what’s going to happen.
“You only have to work every day and not think too much about what might happen. That’s my experience.
“If something negative happens you accept it and go back home. But hopefully not.
“My idea is to be here playing and competing well.”