Hull KR do not expect James Greenwood to play again in 2019 after the second row forward suffered a ruptured anterior cruciate knee ligament.
The former Wigan player sustained the injury just minutes after his introduction as a substitute in Sunday's 10-6 win at in-form Wakefield and scans have confirmed the worst fears of coach Tim Sheens.
The club say the 27-year-old Greenwood, who is out of contract at the end of the season, will undergo surgery in the coming weeks.
A statement said: "The club can confirm that James Greenwood has undergone scans following an injury sustained in last weekend's game against Wakefield Trinity.
"The second row was helped from the field and did not return to action during the round five tie.
"Scans have confirmed that he has ruptured his anterior cruciate ligament and will have surgery in the coming weeks. He is not expected to feature again in 2019."
Hull KR have also announced that forward Ryan Lannon, signed from Salford in the winter, will be out for ten weeks following ankle surgery.