Manu - a two-time premiership winner with Easts - was unveiled as the Chiefs' seventh big-name signing for their inaugural season in 2028 earlier this week.
The 30-year-old will see out the remainder of his contract with Parisian rugby union side Racing before linking up with the Chiefs.
But there is a considerable gap between the end of France's Top 14 season - which typically concludes in late June - and the start of the Chiefs' first pre-season campaign in November 2027.
That could give Manu the chance to refamiliarise himself with rugby league and hand an NRL side the opportunity to add a former Golden Boot winner to their ranks in the lead-in to next year's finals series.
"He's not coming back? I know he's going to PNG. Who knows (about next year)," Robinson joked.
"It's been great for Joey, he has got some adventure going to Japan and France and now PNG.
"He deserves everything he gets, Joey is one of our favourites.
"He'll always be a Rooster, but his adventure has taken him elsewhere and he's always welcome through these doors.
"I haven't spoken to Joey about that (a short-term deal).
"He likes his European holidays now that he's got some culture in him, so we don't know what he's going to do after that Top 14 season. We'll see."
Even without Manu, the Roosters will hope to be a premiership heavyweight in 2027, but their chances of claiming this year's title took a major dent in last week's shock 25-24 loss to Wests Tigers.
Robinson's men have dropped to third and, as it stands, would be the away side in week one of the finals series.
The Roosters face the fourth-placed Dolphins at Allianz Stadium on Saturday where Robinson is hopeful James Tedesco will be cleared to return after a month-long lay-off with a "membrane injury" in his foot.
"We didn't mince our words, but they were really honest and direct which makes it much clearer and then you get to solutions pretty quickly," Robinson said of the Tigers loss.
"It's not what we wanted, that was pretty clear, but it also highlights some things that we've probably been sleeping on and we need to improve.
"So whatever it is you've got to see it as a gift, and then pick it up and move forward."
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