GEELONG will be without No. 1 ruckman Brad Ottens for at least a month with the club confirming he suffered a medial ligament injury to his right knee in the Cats' 20-point win over Richmond on Saturday.

Ottens clashed knees with Tiger ruckman Troy Simmonds in a centre bounce contest late in the first term, and collapsed to the Skilled Stadium turf when his right leg buckled.

Unable to put weight on the leg, he was helped from the ground and did not emerge from the Cats' rooms.

Coach Mark Thompson confirmed after the game that the 29-year-old had sustained a four-to-six week injury.

"It's a better result than we initially thought. We thought he had a posterior cruciate, which is the ruckman's curse," he said.

"You don't like to see it. You know straight away when people can't get to their feet and walk or run [that] they're in a bit of trouble.

"We had our fingers crossed and it's not completely bad news."

Ottens had three hit-outs and two disposals to his name and was involved in the Cats' fourth goal, finding teammate Travis Varcoe deep in attack, shortly before the injury occurred.

While the Cats appeared to struggle after Ottens left the field, Thompson said he was confident the side would not suffer without him.

"He didn't play until round 10 last year and we didn't lose a game in the 10 rounds he didn't play," he said.

"That's the beauty of our team. It creates opportunity for the young guys to get a few games, and we'll cope okay without him.

"Blakey (Mark Blake) now gets elevated and we've got to pick one of the young ruckmen we have.

"We've got five of them on our list. Unfortunately two got injured in the reserves as well.

"We've got enough depth there. It will come out of guys like Trent West and Shane Mumford."

Thompson confirmed the Cats' first-round draft pick Mitch Brown suffered a season-ending broken leg in the VFL side in Saturday afternoon's curtain-raiser.

The young gun snapped his leg in a tackle and Thompson claimed his light frame would have contributed to his susceptibility to such an injury.

"He's our No.1 draft pick so we're really disappointed with that," Thompson said of the injury.

"It will give us a chance for us to work on his body and get him a bit stronger.

"It's a really physical, brutal game and it just reinforces some of the young players coming in, we should probably look after them a bit more."