THE FA have launched an investigation after Exeter made an illegal substitution in last night’s replay, the Telegraph & Argus understands.

The Grecians made a sixth change – one more than allowed - when they brought on Josh Key for Sam Nombe at the start of extra-time.

They went on to win the tie 3-0 at St James Park with all three goals coming from subs – Matt Jay getting two and Nigel Atangana also netting.

City have been invited to provide their comments to the governing body, who could decide to overturn the result.

The competition rules state that clubs “may use five ... substitute players at any time in a match (including during any period of extra-time).”

Clubs are permitted a further opportunity to make a sub during extra-time – but not go above the five-change limit.

An outcome is expected to be announced by the end of the week.

As it stands, Exeter are due to travel to Cambridge in rouund two on December 4.