The San Francisco 49ers head into their biggest game of the season. The team is undefeated, atop the NFC West standings, and hopes to remain there.

This weekend's matchup might also be the biggest of the season for the 49ers' opponent, the Los Angeles Rams. The division rival is coming off two straight losses after winning its first three games and is desperate to turn things around. That makes the team dangerous, and 49ers defensive coordinator Robert Saleh knows that.

There has been a lot of talk about the possible regression of the Rams. It was just eight months ago that they were playing in the Super Bowl. Now, at 3-2, they appear to be sliding.

Saleh isn't buying into that talk and knows exactly what the Rams are.

"They're very talented," Saleh told reporters on Thursday. "All this narrative that they've taken a step back, I don't see it. They're putting up points at a rapid rate. Their drop-back game is better than I've ever seen it. Their play-action pass and run game is still there. Sean (McVay) and his staff are still doing an unbelievable job calling plays, setting things up."

Whether or not they have regressed, the Rams might be the best team the 49ers are going to face through six weeks of football. The national media knows that, and that's why it isn't quick to pick San Francisco as the favorite to win on Sunday.

"It's a great challenge for us," Saleh continued. "It doesn't matter who we have on the football field because schematically and team-wise, this is by far our greatest challenge."

The 49ers may still have their lingering doubters, as they have had all season. Yet, they are 4-0. The offense, however, is limping into the division showdown. The team will be without both of its starting tackles, Joe Staley and Mike McGlinchey, and its only fullback, Kyle Juszczyk.

The injuries on offense will have little impact on Saleh and his defensive game plan.

"It is a team football game, but from our mindset, we're trying to approach everything and be our absolute best every single play," Saleh said. "Whatever is happening on offense, it shouldn't ever have an effect on what we do defensively."

The 49ers and Rams kick off at 1:05 p.m. on Sunday from the Los Angeles Memorial Coliseum.