You'll have to find me an instance of a team knowingly signing a player with a broken leg. I've never heard of it. They'd be better off waiting for player to recover and then signing him because they wouldn't have to cover his wages when injured.
If he wasn't injured for the long term he'd absolutely be worth 20-30m though injury prone or not.
Also this is sort of interesting regarding the injury:
The main function of the fibula bone is as a point of attachment for many of the muscles of the lower leg. The tibia is the weight bearing bone of the two whereas the fibula has much of its surface for muscle attachment. This results in traction and twisting forces placed on the bone from the surrounding muscles which over time cause a stress fracture.
Athletes with excessive pronation or rolling in of the feet when running are more susceptible because the peroneal muscles must work harder for longer during toe off in the running gait cycle.