The Portuguese defender tested postive for dianabol following Boro's UEFA Cup game in Xanthi at the end of September.
A hearing will be set to hear his appeal, propably in the New Year. Xavier has continually protested his innocence claiming he took the drug unknowingly through a contaminated supplement.
A decision as to his future at Boro has not been announced, but if the appeal is unsuccessful the club could cancel his contract.