Garry Monk has left his position as Middlesbrough boss two days before Christmas, despite winning at Sheffield Wednesday hours earlier.
The 38-year-old former Swansea and Leeds boss was appointed in June, but Boro are well adrift of the target of automatic promotion.
Tony Pulis, out of work since leaving West Brom in November, is an experienced name already linked with the vacancy.
"Middlesbrough Football Club have parted company with manager Garry Monk," Boro announced.
"The club would like to thank Garry for all his hard work and dedication, and wish him all the best for the future.
"The club's academy manager Craig Liddle will take temporary charge of first team affairs during the interim period while a successor is appointed."
Monk's departure comes despite the victory at Hillsborough earlier in the day, Boro's 10th win in 23 Championship games this season.
Boro are ninth, three points behind Aston Villa, who occupy the final place in the play-off places.
But the aspiration was to challenge for a place in the Championship's top two this season for an immediate return to the Premier League.
Boro are 12 points behind second-placed Cardiff at the halfway stage of the season.
Monk managed Swansea in the Premier League between 2014 and 2015 before helping Leeds to a seventh-placed finish in the Championship last term.
He was unable to agree an extension to his stay at Leeds under new owner Andrea Radrizzani, leaving last May before swiftly taking up the reins at Boro.
Boro were relegated from the Premier League in May after just five wins under Aitor Karanka and then Steve Agnew.
Middlesbrough play at home to Bolton on Boxing Day and Aston Villa on December 30.