Barnsley midfielder Anderson De Silva will be out for up to seven months after rupturing his anterior cruciate ligament against Norwich last month.
Anderson (right) celebrates the win at Liverpool with boss Simon Davey
The Brazilian, 25, joined the Tykes for an undisclosed six-figure fee from Everton at the end of January, after he had impressed in two loan spells.
But an MRI scan has revealed the injury is much worse than had been expected.
"He is distraught, and we as a club are distraught," Barnsley manager Simon Davey told the club website.
"It is a massive blow for us after chasing him all season.
"We will send the scans through to a consultant who will advise us on the best possible course of action."
Anderson has made a total of 21 appearances for the Tykes, and played in their recent FA Cup victory at Liverpool.