Sydney Roosters prop Lindsay Collins suffered a serious head knock barely 20 minutes into his return from concussion.

Sydney Roosters forward Lindsay Collins could be facing a lengthy stint on the sidelines after suffering another head knock in his first game back from concussion.

In the 27th minute of Thursday night's NRL clash with Manly, Collins clashed heads with Sea Eagles forward Morgan Boyle in a tackle and appeared to be knocked out before he hit the ground.

He was to play no further part in the match, his head clash classified a category one, the most serious grading.

"He was okay in the sheds but it obviously looked quite bad," said Roosters coach Trent Robinson.

Collins suffered a serious head knock at the start of last season and needed to leave the field in a medi-cab.

More recently, he missed rounds 18 and 19 this season after suffering a concussion in the State of Origin decider on July 13.

"It's always disappointing to see (concussion) happen to one of your players, especially when it happened a couple of weeks ago," Robinson said.

The Roosters are noted for careful handling of concussion cases. In 2021, repeated head knocks prompted veterans Jake Friend and Boyd Cordner to retire from the game after lengthy sideline stints.

More recently, playmaker Luke Keary spent over a month on the sidelines after suffering a head knock against Melbourne in round 14.