Second Heat by Preston Walker

When omega wolves must prove themselves in blood.
Nico is the young, unwanted omega son of a pair of alpha wolves. Like all other omegas, he was thrown into the fighting pit to prove himself and find an alpha mate. Too bad it hasn’t worked out like that. Nico’s been in the pit for longer than he’d care to remember. Life’s nothing but a struggle for survival, until a new locker room doctor shows up.
Mick is an older alpha werewolf, talented in fixing what ails the body and the heart. On assignment from his pack alpha, Deacon, he’s been sent to spy and cause subterfuge within the omega fighting circuit. A rare wolf doctor, Mick is quickly hired by the pit with clear instructions: do only enough to keep them alive.
But when Mick’s eye is caught by a ferocious, gorgeous omega, he’ll do whatever it takes to save him. Even if it means revealing what he’s really there for.