Navas has clocked 10.8sec for 100 metres.
"We used to do tests at Sevilla and I came out the quickest," he said. "I don't know about City - we haven't done any speed tests!
"I know I can provide width and speed to get around the back. I don't think it's any more physical in England than Spain. When you are a tricky wide player, you are always used to tackles and challenges.
"Defenders are always tough, whether you play in Spain or England. The difference for me has been the speed and tempo of the game."