Collingwood forward Daniel McStay has been ruled out of the AFL grand final after suffering a high-grade medial injury in the Magpies' pulsating one-point win over the Giants in the first preliminary final.

McStay kicked two goals in the Magpies' thrilling one-point preliminary final win over GWS at the MCG on Friday night.

He injured his right knee during the third quarter of the 8.10 (58) to 8.9 (57) victory and was ruled out at the final change when the match still hung in the balance.

"It's unfortunate to confirm that Dan has sustained a high-grade medial ligament injury during last night's preliminary final with an expected recovery time of six to eight weeks," Collingwood's GM of football Graham Wright said.

"Dan has been an important part of our season this year and played an integral role in the last night's victory against the Giants.

"We are all disappointed for Dan to miss the grand final, but we will all rally around him, and he will continue to be a part of the team's preparations for the week ahead."

The 28-year-old had scans on his injured knee on Saturday morning.

"It's pretty scary so close to playing in a granny (grand final) and it might have been taken away from me, so we will wait and see," McStay told reporters before the scan results came back in.

"Obviously for myself, it's a bit of mixed emotions but I'm just incredibly proud of the boys and the way they played last night and the way they were able to shut the game down."

After the match, Magpies coach Craig McRae said he feared McStay would miss the grand final.

I don't want to put a definite decision on it but I think he might be unlucky to miss out. We'll wait and see," McRae said on Friday night.

"That'll play out pretty quickly, I would've thought."