Anderson made the comments Tuesday on FS1's Undisputed. Gurley -- a two-time All-Pro and the 2017 AP Offensive Player of the Year -- had just 10 carries for 35 yards in the Rams' 13-3 loss to the New England Patriots in Super Bowl LIII.
He had just one carry in the first quarter.
Anderson signed with the Rams in December and started in place of Gurley during the team's final two regular season games.
"He was more hurt than what we thought," Anderson said. "The injury was a little bit more than what everybody in the building thought, including himself."
The three-time Pro Bowl selection had 1,251 yards and a league-best 17 rushing scores and 21 total touchdowns in 14 starts this season.
Anderson also struggled against the Patriots, running for 22 yards on seven carries in the loss. The six-year veteran -- who has also had knee issues -- said once you have a knee injury, you always have a knee injury.
"I would say a sprained knee," Anderson said. "Obviously it was the same injury he had before in his career."
Rams coach Sean McVay said after the Super Bowl that he did not expect Gurley to undergo any knee procedures during the offseason.
"As far as I'm concerned and as far as I know, that isn't the case where we're planning to do anything like that," McVay told reporters.
Gurley was not listed on injury reports before the game.
"Todd is healthy, and we just didn't really get a chance to get anybody going today offensively and that starts with me," McVay said after the Rams' loss.
Gurley was bothered by a left knee issue after Week 1 of the 2018 season, before another knee issue surfaced in Week 15. The Rams star signed a four-year, $60 million extension with the franchise last offseason, making him the highest-paid running back in NFL history. The deal included $45 million guaranteed.