The Crows forward sat out most of Saturday night's loss to Carlton at the MCG after landing awkwardly after a marking contest in the first quarter.
He immediately left the field and was subbed out of the contest before returning to the bench on crutches with ice on his right knee.
There were some hopes throughout the game that Walker had escaped damage to his anterior cruciate ligament and may have suffered harm to his posterior cruciate.
However, Crows coach Brenton Sanderson said the club needed to wait to see the results of scans.
"There's speculation I know in our changerooms and of course through the media too but things will become a bit clearer for us on Monday when he has his scans," Sanderson said after the 32-point loss to the Blues.
"You always hate losing one of your best players early in a match but fingers crossed that it's not long-term."
Sanderson said there was still uncertainty surrounding the severity of Walker's injury.
"I've heard everything since I've been back in the change-rooms. I've heard everything from worst case to he could play next week. It would be foolish for me to comment too much further on it until we know exactly what's going on," he said.
"It's a big story obviously for our footy club and hopefully he's not out too long."
Walker looked in ominous form before the injury, taking four first-quarter marks and being his side's single goalkicker for the term.
The Crows moved Andy Otten and Matthew Jaensch forward in a makeshift attack after Walker left the field, and both kicked three goals each.
The second-year coach admitted Walker was perhaps the player the club could least afford to lose.
"When we do our 'What if?' meetings the day before the game, we don't like it when we lose a key forward. That becomes pretty much panic stations. We got that today early and the coaches did a good job to shuffle things around," Sanderson said.
The loss leaves the Crows with only two wins ahead of a difficult clash with Hawthorn next Saturday.
The Crows matched the Blues with 11 goals after quarter-time but conceded 64 inside-50 entries and had 41 fewer contested possessions.
Midfielder Rory Sloane, one of the Crows best players for the game with 19 disposals, said he felt the team had "let people down" with its performance.
"It's really hard, especially with the build-up we had and [it being] Anzac [Day] week. It's hard not to feel a little bit angry and a little bit emotional," Sloane said.
"Just personally I feel like [we] let a few people down. There are a lot of emotions going but you've got to quickly get rid of them and come Monday and Tuesday we've got to get back up and going and get ready for Hawthorn."
