THERE was a time when a serious injury for Shane Mumford would have sent shudders through the Greater Western Sydney camp.

But Rory Lobb has spent the past two years making sure the AFL's best big men don't think they're in for a day out when they take on the Giants without 'Mummy' in the line-up.

Lobb got a serious wake-up call in round 12, 2015, a week after Mumford went down with a season-ending ankle injury, when the young West Australian was handed the task of taking on North Melbourne star Todd Goldstein.

The Kangaroo, on the way to All Australian selection that season, broke the League record with 80 hitouts that afternoon at Spotless Stadium, and set a new mark for hitouts to advantage.

Lobb was out of his depth and knew it, but he was the Giants' only real option. Two years on, Lobb told he had to get schooled by Goldstein to learn the lessons he needed to become the player he is today.

"Obviously I wasn't too happy with that first effort, but three games into my AFL career I wasn't really ready for it," he said.

As a 22-year-old, Lobb played eight more games in 2015 as the Giants' finals hopes fell away. It gave him a taste of senior footy, and his response was outstanding.

Lobb returned early from his off-season break to hit the gym, and by the time the 2016 season came around he'd added bulk to his frame, which gave him the confidence he needed.

Playing mostly as a tall forward, Lobb played all 24 games for GWS last year, took the second-most contested marks in the competition (just two fewer than Gold Coast star Tom Lynch) and kicked 29 goals.

Come this season, and with Mumford ruled out of the finals with a foot injury, the Giants once again turned to Lobb, and the result was much different in last week's semi-final win over West Coast.

Lobb had 39 hitouts opposed to Nathan Vardy and Drew Petrie, with help from Jonathon Patton, to be one of the Giants' key winners on the night.

"I really had a point to prove and I had to put my best foot forward to give our midfielders first use of the footy," he said.

"I think I still need to add a few more kilos to be a No.1 ruckman, but I felt great out there.

"My running ability is pretty good given I've played on the wing a fair bit and I copped a few more bumps and bruises which wears you out, but all in all I was really happy with the way it went."

Lobb faces another big test against Richmond at the MCG on Saturday, but has some familiarity with opponent Toby Nankervis, who has been one of the recruits of the season after crossing from Sydney.

The pair of young big men crossed paths on multiple occasions playing in the NEAFL when Nankervis was at the Swans. It won't be a clash of developing ruckman this time around, and Lobb is ready for the challenge.

"If I get the sole ruck role again, my midfielders expect me to either win or halve every contest, so it's going to be a huge battle," he said.

"You've got to mix it up as much as possible, because you don't want an opposition ruckman getting a fix on you or the way you ruck.

"I need to nullify him to make sure we can win the ball at the contest, but obviously he's a very good player. I have to make sure I get the job done."