The injury has allowed Patel to return to the squad for the first time in over two years, and the 30-year-old was quick to reveal his surprise.
"I was not expecting a Test call," he told BBC Radio Nottingham.
"I thought the door was closed on Test cricket. It's unfortunate for Zafar but I have to make the most of it.
"I think I will be behind Moeen and Rash to play, but I am just happy to get on the trip. I was planning to go on holiday to Dubai next week, so this is a pleasant surprise."
Patel has scored 109 runs and taken four wickets in his five Test matches.