Sunderland will be backed by a sold-out away end at Sheffield United and Nottingham Forest.
And club legend Kevin Ball has hailed the "fantastic" Sunderland support.
Chris Coleman takes his Sunderland side to Bramall Lane on Boxing Day to face Chris Wilder's Sheffield United, with more than 2,000 supporters backing the Black Cats.
Sunderland then head to the City Ground on Saturday with a busy festive week on the road for the squad and supporters.
A club statement read: "Both of Sunderland's festive away days have sold out.
"Following their run of three games unbeaten, the Black Cats are set to be backed by sold out away ends at both the game at Bramall Lane to face Sheffield United on Boxing Day and the clash at Nottingham Forest on Saturday 30 December."
Ball, former captain, coach and now ambassador, said: "Boxing Day we're at Bramall Lane and we will have over 2,000 fans travelling there, which is fantastic backing.
"I have some brilliant memories of playing down there, scoring goals, getting sent-off, all sorts! But it is a fantastic football ground and it will be rocking on Boxing Day."