"I don't know," Nadal said when asked about his chances of playing the unseeded 27-year-old Kyrgios.
"Honestly, I can't give you a clear answer because if I gave you a clear answer and tomorrow another thing happens, I will be a liar."
Nadal took a medical timeout against 11th-seeded Fritz during his quarter-final outing to get treatment on the injury and said he had to adjust his game to continue playing.
The Spaniard, however, considered retiring many times during the contest.
"I just wanted to give myself a chance. Not easy to leave the tournament, not easy to leave Wimbledon, even if the pain was hard," the 22-times Grand Slam winner said.
"I don't know. I wanted to finish. I fought. Proud about the fighting spirit and the way that I managed to be competitive under that condition."
Nadal said he was worried about the injury and he will undergo more scans on Thursday before making a decision about continuing to compete at the grasscourt major.
"I am used to holding pain and play with problems," said Nadal, who played and won Roland Garros with pain-killing injections prior to each match and only confirmed his Wimbledon participation after radio frequency treatment eased pain in his foot.
"Knowing that, when I feel something like I felt, that is because something is not going the proper way in abdomen. But let's see. I had these feelings for a couple of days. Without a doubt, today was the worst day, has been an important increase of pain and limitation," he said.