Osasuna will aim to continue their recent resurgence against a wildly unpredictable Rayo Vallecano side.
Los Rojillos are still 19th but have went three games without defeat in La Liga and carried that form into the Copa del Rey midweek, turning round a 1-0 deficit to defeat Sporting Gijon 2-1 on aggregate.
“We knew it was going to be hard work, but we deserved to progress to the next round,” said boss Jose Luis Mendilibar.
Rayo are flying high, eighth in the standings after last weekend’s 2-0 win over Real Mallorca, but Paco Jemez’s side have been a bit erratic on their travels, losing 4-0 to Real Sociedad on their last trip to the north.
“Osasuna are one of the most intense teams I've seen this season, and that alone is going to make it difficult,” cautioned Jemez ahead of the Friday night kick-off. “I do not know why they’re down there.”
Kick off: Friday November 30, 20.00 (BST)