The world number one suffered the injury in the first set of Monday's last 16 win over Argentina's Juan Martin del Potro and immediately revealed that his future participation in the tournament was in doubt.
But the 25-year-old revealed on his Facebook page that he will be fit to tackle Fish on Wednesday.
"Yesterday after the match I went to take an MRI at a London hospital," he said.
"During the match I thought I had something serious. But as the match went on the pain got better and thankfully the tests don't show an injury.
"Today I will practice at 4:30pm and I'll play tomorrow. Thanks all for the support."
Nadal needed to have his left foot taped at 6-6 in the first set tie-break of Monday's Centre Court clash - won 7-6 (8-6), 3-6, 7-6 (7-4), 6-4 by Nadal - and told reporters after the match he was not optimistic about playing on Wednesday.
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