This is a firm bunion spacer that should keep your toe in position. Your sock is what keeps it in place, so a snug-fitting sock is best. I'm really not sure how well it will stay in place with the side to side motion tennis requires, but I doubt a blister will develop. If anything, the toe separator would just slip out of place. You may be able to keep it in place with some Coflex (product #829); splinting the 1st and 2nd toes together with the toe separator in between.