Wayne Carey says last night was a "bit of a wake up call" for GWS.
GWS lost a crucial clash to St Kilda on Friday night, leaving them with a 5-2 record this season.
Duck believes the Giants will "still" finish in the top four, but suggested on the Saturday Rub they need to learn to deal with the sort of pressure St Kilda brought on Friday night.
"For such a talented team, when they're under pressure, I thought this might be the making of them," he said on Triple M.
"Once again last night, they had their moments when they were able to get out and play that skilful brand. But St Kilda brought their A-grade pressure, they tackled ferociously.
"Right now, you've have to say, GWS...they don't get it their own way, they struggle. And under extreme pressure, there's some question marks that are now being asked."
Duck said the Giants are significantly talented, but says all the work now is "above the shoulders".
"They are massively talented, we already know that. It's all above the shoulders for me," he said.
"I said this when they lost by a kick in the preliminary final last year: if they think they’re just going to roll up in 2017, BT, and win the flag or finish top four, they are kidding themselves.
"I think they're getting a little bit of a wake up call already this year to say, yeah we're talented, but if we don't really prepare properly...the competition's that close, you get sat on your bum, and that's exactly what happened to them again last night."