Speaking on Wednesday morning, prop Jason King – himself a long-serving veteran of the Brookvale outfit – said the players were "devastated" to see their mate leave.
"He's a crucial member of our team and integral to a lot of success we've had over the years," King said.
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"Souths are certainly getting a very good footballer and a top bloke as well, so I guess come the end of the year we'll be a bit devastated that he's leaving but wish him all the best."
WATCH: George Burgess welcomes Stewart signing
King also said it was disappointing there aren't more structures in place that allow clubs to keep long-serving players.
"We've got a few guys similar to Glenn at the club that have been here a long time. It's disappointing that for the sake of two of three years at the back end of players' careers that they can't stay one-club players," he said.
Winger David Williams said it will be a huge loss for the club but he wished Stewart all the best for the future.
"It's a big loss for the team, he's a quality player and he's a great person to have around the club but it's great that he's got somewhere to continue his career," Williams said.
"We're happy for him, it's good that he's looked after for the next couple of years."
Halfback Daly Cherry-Evans said the players are glad Stewart had his future sorted out and now the club could move forward.
Prop Josh Starling, who joined Manly from Stewart's future club the Rabbitohs at the end of last season, said he will fit in well at his new club.
"It's a bit disappointing but I've been over at Souths and he's going to have a good run there, he's going to like it, so all the best to him," Starling said.
"He's a good player, he'll make a difference anywhere he goes. Souths are very lucky to get a good footballer."