Grundy was substituted out of the game midway through the third quarter after hyperextending his neck in a marking contest on the wing.
The hyperextension caused a pinched nerve which resulted in Grundy feeling severe pain through the back of his shoulder.
Grundy has dealt with nerve pain over the past few seasons, stemming from a serious neck injury he sustained in a training incident back in 2015.
The injury comes at an extremely inopportune time for both Grundy and the 2-8 Magpies, with the 27-year-old rediscovering some of his best football this season.
Grundy will join star midfielder Taylor Adams on the sidelines, with Adams also given a two-to-three week recovery period after injuring his knee in Round 10 against Port Adelaide.
According to the club, scans revealed a “minor” tear which will be worked on over the next fortnight as Adams sits out.
The Grundy and Adams-less Collingwood is currently scheduled to face the Adelaide Crows in Adelaide in Round 12, before a bye in Round 13.