The star centre, who played fullback in the 32 points to 8 win over the Wests Tigers as the tri-colours kept their finals chances alive, lasted just 24 minutes before hobbling from the field with a suspected hamstring injury.
Last year's Golden Boot winner had been filling in at the back for James Tedesco, who missed the game against the Tigers with a concussion, and, given his history of head knocks, is no guarantee of playing against the South Sydney Rabbitohs next weekend.
It could leave the Roosters looking at a third-string fullback option.
"It's mild, but he still had the leave the field so it's never a good sign," Robinson said during his post-match press conference.
The NRL Physio said it looked a "pretty typical hamstring strain" and that he would be unlikely to play next weekend against the Rabbitohs.
Pretty typical hamstring strain mechanism for Joey Manu - running in forward lean position putting hamstring on stretch. Would be surprised to see him back tonight & even a minor strain would put him at long odds for next week
— NRL PHYSIO (@nrlphysio) August 26, 2023
The Roosters have just six days on their turnaround before taking on the Rabbitohs in the crunch game.
"It's just eight stitches and a bit of a shiner [for Radley]," Robinson added.
"Billy [Smith] got a poke in the eye and he will have a bit of a shiner as well."
Robinson was also quizzed on Brandon Smith who had appeared to come from the field with a shoulder injury, but the coach said it was a stringer and he was also fine.
"No, that was okay, it was a stinger. I took him off when Sam [Walker] came back on the field, so Sandon went in and then I think Billy went down a minute and a half after that, so he [Smith] went straight back out there," Robinson said on the off-season recruit.