Sam Morsy is available for selection for Saturday's match against Birmingham City.
The midfielder was shown a red card during Wednesday night's 1-0 win over Luton Town at the Riverside.
But a successful appeal from Boro means his one-match suspension has been rescinded.
An FA statement reads:
"Sam Morsy will be available for Middlesbrough FC’s next game after a successful claim of wrongful dismissal.
The midfielder was sent off for denying an obvious goalscoring opportunity during an EFL Championship game against Luton Town FC on Wednesday [16/12/20]."