The Albion take on the Saints on Monday night, and they must be able to deal with the dead ball danger of Ward-Prowse.
The Englishman scored a free-kick and had an assist off a set piece against Manchester United last weekend.
Potter told reporters: "If you have seen Southampton recently, you can see how dangerous he is from corners and free-kicks. He's probably the best in the league at the moment.
"His quality is there. They have some physical, big players who can attack the ball as well.
"Southampton have that string to their bow and they're very good in those situations. We have to be mindful of that."