An orthopedic surgeon cleared Reid of structural damage but he will definitely miss Saturday night's round-three pre-season cup match against Brisbane.
The winner of that match is a near certainty to play in the final.
The 22-year-old All Australian was subbed out in the third quarter after he landed awkwardly on his right knee.
"The outcome of today's medical assessment is positive," Magpies football manager Geoff Walsh said in a statement.
"Ben won't play this week but beyond that we don't feel it will cause any interruption to his season."