The injury came at a particularly inopportune time, as the 209cm giant had finally grabbed the mantle of the Cats' No.1 ruckman after playing just five games in his first five seasons at the club.
"It was crushing for me, being a sixth-year player then, as I hadn't made my mark yet," Simpson, who turns 25 next month, told AFL.com.au.
"It was pretty crushing for my confidence. It had been good to be in the team and playing well.
"Hamish (McIntosh) was down, and I felt like I grabbed that spot and was playing well enough to stay in the team.
"We had some dynamics in the middle and around the ground we were getting my hands on the ball and getting some better numbers at the stoppages.
"But I knew as soon as I did my knee that that was the season for me … that the opportunity was gone from that point.
"Seeing the boys going into the finals, I was on the outside and the boys were a chance to win the premiership again.
"That was the hardest thing for me to deal with."
Fast-forward five months and Simpson is now in a much better frame of mind.
His knee has recovered well from the surgery needed to repair the damage, and he is steadily increasing his training load as the NAB Challenge nears.
"I started my rehab before the season finished last year," he explained.
"Even pre-Christmas I was running and doing a little bit of the training – sort of half the drills.
"I was just getting my knee right, so that in January I could have a big hit, and it's worked. It's been a good program for me. I'm getting some good k's in the legs now."
Over the summer, Simpson has formed a friendly but competitive rivalry with another of Geelong's big men on the comeback trail, former Kangaroo McIntosh.
He didn't play a game at any level last season, due to a number of leg and foot injuries, but he and Simpson have been impressive performers on the track in recent weeks.
"Big Hamish is up and about, which is good," Simpson said. "It's good competition and great to get out there and push for that spot.
"All the big blokes, we all get along really well. We're all really close mates, so it's a good, fun rivalry.
"Hopefully there might be a time when they can play the two of us. I don't know what Scotty's thinking, but if we're both up and playing well, there's no reason why we couldn't.
"Hamish has been a really good forward at North, so hopefully they can squeeze us both in there."
Simpson is keen to be part of the Cats' NAB Challenge opener against Collingwood at Simonds Stadium on February 20.
However, the club's fitness coaches are set to take a conservative approach with his pre-season program.
"If there are no other setbacks, I'll be right for selection," Simpson said.
"It's whether they want to hold me back a bit or give me an extended pre-season.
"We're just going to see how I'm going."
Twitter: @AFL_AdamMcNicol
