Adelaide forward Shane McAdam's horror season has continued, with a thigh injury to sideline him for up to six weeks.

McAdam copped a three-match suspension for rough conduct in the opening round and has been out of AFL ranks since.

He picked up the injury in the state league a week ago, with the Crows now saying he will miss between four and six weeks with a quadricep strain.

Adelaide travel to play reigning premiers Geelong in Geelong on Saturday as they seek to rebound from a one-point loss to Collingwood, described by ruckman Reilly O'Brien as the toughest defeat in his 84 AFL games.

The Crows led for all but 21 seconds against the Magpies, who kicked the last three goals to snatch victory.

"It sat in the guts pretty badly," O'Brien told reporters on Tuesday.

"It's probably the most disappointing loss I have ever been a part of in terms of how flat I felt after the game and how flat we all felt as a collective"

O'Brien said Adelaide's match review of the loss triggered some "hard conversations".

"We just went away from the way we want to play, in that last quarter in particular," he said.

"We didn't get it done around the stoppage and in the contest but also were a little bit safe with the ball, and then we didn't defend the way we would have liked.

"We just fell away from what we wanted to do. Our mindset probably went a bit too defensive.

"Losing like that is very deflating for everyone.

"In the past we might have (said) 'honourable loss', but we have certainly gone well past that stage now. We expect to win."

O'Brien said the Crows would take that winning expectation into their trip to Geelong for an away fixture he rated as the hardest in the competition.

"The good thing is it's a great challenge and we love a challenge so I'm pretty excited for it," he said.

"They're probably going to be expected to win down there at Kardinia Park.

"But we will go in with a mindset of taking it right up to them and getting it done, because we expect to win every week and this week is no different."