The prognosis after seeing the specialist was to have an immediate operation which he's had, and he's expected to be out of first team action for at least two months.
The injury comes as a blow to Lynch who had settled into the right back slot well since his summer move from Yeovil Town.
Boss Mark Robins told Radio Sheffield yesterday that the op. had to happen sooner rather than later, as leaving the problem could result in further damage and a lay off of upto five months.
Meanwhile Danny Harrison is a doubt for tomorrow's game with Grimsby with a groin injury, we'll have full team news and match preview later.