Aitor Karanka has paid the price for his side's limp attack, becoming the sixth Premier League managerial casualty this season.
In a statement on their official website, Middlesbrough revealed that both they and Karanka agreed it was in the "best interests" of the club to part company.
Middlesbrough's board have now chose to look for a new man to lead them to survival in the final few months of the Premier League season. "We wish him all the best for the future", a statement read. "This club will always hold a special place for me and I wish everyone connected with Middlesbrough Football Club the very best for the future".
Middlesbrough are 19th in the Premier League, with a game in hand over Hull City, who are two points above them but three adrift of 17th-placed Crystal Palace.
Middlesbrough goalkeeper Victor Valdes has expressed his gratitude towards Aitor Karanka after he left the Riverside Stadium on Thursday.
Agnew will take charge of Sunday's big home clash against Manchester United, who are on an unbeaten 17-match league run but will be without suspended top scorer Zlatan Ibrahimovic.
Karanka guided Middlesbrough to promotion last summer as they finished second in the Championship, a year after narrowly missing out by losing in the playoff final to Norwich.
Karanka's last game in charge was a 0-2 loss to Manchester City in the FA Cup on Saturday.
Boro fans then posted their reactions to this news, with some feeling gutted and thanking their now former boss for the memories.
His departure may come as a relief to some of those men, but the club remain in a parlous position with time fast running out.