The Roosters attempted to have Watson cleared to play in Sunday's season decider after he suffering a head knock during his side's preliminary final win over the Dolphins.
Under NRL concussion guidelines, players cannot return to play inside 11 days and despite responding well, Watson was pulled from the Roosters' squad on Friday after meeting with specialists.
Many pundits this week have argued for a fortnight's break between the preliminary finals and the grand final, which would have given Watson the chance to line up in his final Roosters game before joining St George Illawarra.
But Robinson said he was not in favour of such a move.
"These are unfortunate things that happen, but we have protocols for a reason," the Roosters coach said at Accor Stadium on Saturday.
"I'm more for the week off before the finals than I am before the grand final.
"I feel like momentum's built throughout the final series and the attrition part of it is a part of our game."
Watson, who will be replaced in Robinson's 19-man squad by hooker Benaiah Ioelu, becomes the first player to miss a grand final due to the concussion since the NRL implemented new rules at the start of the 2023 season.
The 30-year-old, who spent four seasons with Newcastle, is one of the Roosters' most popular characters and was informed of his exclusion from the grand final squad during training on Friday.
"Connor's a good man, a strong man, he's his own man, and so he had to sort of control all that - he knew we were in the middle of a session," Robinson said.
"The absolute devastation that it is for him, all the work that's gone into his career for him and his family and friends - then you get the news like that (and) it's quite tough.
"But then he spoke to the group quite clearly about (how) this is about the group.
"Then the player that took his spot in the 19, Benaiah, spoke about the love for Connor and what it means for his role coming into the team."
Robinson is aiming to win a fourth premiership at the club, having last tasted grand final glory seven years ago.
Five members of the 2019 premiership-winning squad remain, with a young core, headlined by 24-year-old halfback Sam Walker, gunning to win their first NRL title.
Veteran five-eighth Daly Cherry-Evans will partner Walker, who Robinson described as a "free spirit".
"He's quite young for a half the age that he is, and he's been moulding his game," Robinson said.
"We've been moulding our team to his game and it takes some time and we're ready.
