Depends...
Your company may require a valid medical.
The examiner may want to see a valid medical.
A medical certificate is required to act as PIC, under EASA & FAA.
EASA (or at least UK CAA, acting under) requires a valid medical for any “licensing action” (endorsing/adding a rating; change of name/address/nationality; or correcting the Instructor privileges that they mistakenly omitted on earlier issue)
FAA used to require a Class 3 for ATP issue, but not the Sim check-ride.
EASA also does not require a valid medical for a Class Rating in an aeroplane (not acting as PIC).
Hope this helps.