Pennant joined the Potters last summer from Real Zaragoza in a £2million deal after an initial loan move.
He said: "Coming back to England and the Premier League, I never even dreamed I'd be playing at Wembley.
"I've never played there before and it was never in my thinking when I signed here.
"We've got eight League games left and we've got to keep our focus. We can't let Wembley distract us."