Off-the-top-of-my-head reaction: I would go to the teacher, tell him my daughter is feeling pressured by him, and ask him to lay off - I would not take any excuses from him. If he wouldn't listen, I'd go over his head.
You don't say if this teacher is the school track coach - actually, you say something about not being sure. At any rate, he's being foolish at best, and something else at worst. He's not encouraging her to go out for track - he's making her uncomfortable about her running and about herself. Teachers ought to know that seventh-graders will take things personally if they can - it's their nature.
If your girl decides to run track, the school coach will work her out, or you can perhaps find her a coach at a local gym. This teacher does not need to be involved.