Hull's record signing Jimmy Bullard has been ruled out for the rest of the season following knee surgery.
The 30-year-old joined the Tigers in a £5m deal from Fulham last month but has played just 37 minutes of football for the club.
Bullard jarred his knee on his debut against West Ham on 28 January and this week travelled to the United States for an operation.
Bullard spent 16 months on the sidelines after suffering a serious knee injury playing for Fulham in September 2006.
He returned to action to play a key role in the club's escape from relegation last year but left Craven Cottage after failing to agree a new contract.
Hull felt the combative midfielder could play a similarly influential role in the second half of their first season in the Barclays Premier League.
City's form has dipped since a bright start to the campaign and the club are just six points above the bottom three after winning just one of their last 16 games.
Bullard's latest injury has proved far worse than first feared with the club initially hoping he could recover with rest.
Scans first suggested the player did not need surgery but after suffering further discomfort, Bullard this week travelled to the Colorado clinic of Dr Richard Steadman where he had his first operation.
A club statement read: "Jimmy Bullard underwent a procedure last night in America to repair a torn cartilage.
"Whilst performing the arthroscopy, the surgeon noticed fresh damage to his anterior cruciate ligament.
"In the best interests of both the player and Hull City Football Club it was decided to undertake a reconstruction of the damaged ligament which means that Jimmy will be unavailable for the remainder of this season.
"The club wishes Jimmy a speedy recovery and look forward to his return in a Tigers' shirt as soon as possible."
Bullard has signed a four-and-a-half-year contract at the KC Stadium.