The pair came through the ranks together at Tottenham before Clyne switched to Crystal Palace, where they came up against each other many times.
They have also been team-mates for the England Under-19s and Under-21s.
And Townsend told The Sun: "We've known each other since we were 3ft tall! Every time I've played against him, he's performed well.
"We both know each other's games inside out so it's going to be a tough battle. Hopefully, I can chuck in a few surprises for him."