Sydney Roosters playmaker Luke Keary will be back for the NRL finals but scans on Monday confirmed he has a left knee medial strain and he'll miss up to four weeks.
It's mixed news for the third-placed Roosters, who are locked in a battle to secure the advantages of a top-four or even top-two spot on the ladder.
The 26-year-old suffered the injury in Sunday's 32-16 win over St George Illawarra.
Rookie Sean O'Sullivan seems most likely to replace him over the next month, although utility Ryan Matterson is another option for coach Trent Robinson.
The Roosters are at home this weekend against struggling North Queensland but then play fellow top-two aspirants South Sydney, before a trip to Canberra and a home clash with seventh-placed Brisbane.
Keary is then expected to return for the final match of the regular season against wooden spoon contenders Parramatta
"He's a huge part of the side. The way he runs and attacks alongside Cooper Cronk; he's a huge part of our team," Roosters lock Issac Liu told reporters on Monday morning.
"But we've got players there who can fill in and do the job."
Meanwhile the Roosters confirmed Dylan Napa is expected to return from his own medial strain in Saturday night's clash with the Cowboys.