Under the current deal, more than 90 per cent of GMS practices rely on the MPIG to top up core pay to the level they received under the old Red Book.
The formula review says new MPIGs could be calculated to make sure no practices lose out, or existing correction factors could be retained.
However, if current correction factors were retained, practices that were worse off under the new formula could receive less core pay than they did before the new contract was implemented.
GPC and formula review team member Dr Eric Rose said: 'We would need a new MPIG if the new formula is implemented. Otherwise some practices will find themselves destabilised and could go out of business.'