Feeling the Heat by Michelle Roberts

Kirsten Keller doesn’t know anything about sports or medicine, but when her twin sister begs her to take her place as a physiotherapist for a week, she foolishly accepts.

The hardest part of the job, as it turns out, is trying not to turn into a big pile of goo every time Brad Pritchard looks at her.
He’s a sexy quarterback with an aching shoulder and a bad attitude, but will he also be the engineer of her downfall?
Brad can’t put his finger on what’s off about Katrina. Normally they don’t get along.

In fact, he hates going to see her. But suddenly she’s being charming and friendly—and it’s causing desire to flame within him.
When he discovers her secret, will Brad use it to destroy the sister that he dislikes at the risk of hurting the one he wants?