The 39-year-old, nicknamed 'The Rocket', sustained the injury in a forest in Essex this week and wore a protective brace while beating amateur Daniel Wells 6-2 in the first round.
"I didn't enjoy any of it. It's painful for me to play," said O'Sullivan, who got had to rest his foot on a stool when he sat in his chair.
"I wanted to see what happened. I was hobbling about and I can't get on a shot properly. If it doesn't improve I'm not sure I will play my next match," he was quoted as saying by the BBC.
He is scheduled to play Peter Lines in the second round on Sunday.
O'Sullivan limped into the York Barbican arena and, despite taking painkillers, winced throughout his match against Welshman Wells but managed to triumph despite being pulled back to 2-2.
"It is swelling up and it is painful. I took all the painkillers I could but if it is not better by Sunday then I probably won't play," he said.
"I am absolutely gutted. I am really enjoying my snooker more than ever. To do that through running, I am just really angry with myself.
"I think I will stop running until my snooker career is over. I wanted to see what happened but I was all over the place."