The Green Bay Packers’ preseason opener turned into a night of horrors, and one rookie has a mountain to climb.

Undrafted free agents face daunting odds, making Jamon Dumas-Johnson’s difficult debut all the more devastating. It required a near-perfect preseason to break into the Packers’ competitive linebacker room, but Dumas-Johnson made the worst possible start.

According to Pro Football Focus, the rookie missed four tackles while giving up both of his targets in coverage. It earned him a 25.3 PFF grade, comfortably the Packers’ worst on an evening filled with disappointing performances.

Packers rookie Jamon Dumas-Johnson may have already ended any hopes of making the roster

The opening was there. Free-agent signing Isaiah Simmons had the Packers’ second-worst PFF grade after struggling in coverage. He allowed five catches on six targets for 76 yards in a performance that has undone a strong start to camp.

Beyond Quay Walker, Edgerrin Cooper, and Isaiah McDuffie, the Packers need another linebacker to step up. Second-year Ty’Ron Hopper caught attention with an impressive performance, but Dumas-Johnson could’ve joined the conversation with a good start to the preseason.

It’s a difficult one to come back from.

Everything starts with tackling, and it’s impossible to make a roster and play regular snaps on defense or special teams if you miss tackles.

PFF credited Dumas-Johnson with four missed tackles on Saturday night.

While there were positive performances hidden under the chaos of a disjointed and embarrassing loss, the Packers may need to add reinforcements at multiple positions, including the interior offensive line. Linebacker is another.

Two undrafted rookies — running back Amar Johnson and defensive tackle Nazir Stackhouse — are trending up after the preseason opener.

Johnson built on an impressive summer with a head-turning performance, and while it’s still a long shot for him to clinch a roster spot, he has earned another opportunity to prove himself. Stackhouse is closing in on the 53-man roster after translating excellent work on the practice field into preseason action.

Unfortunately, Dumas-Johnson couldn’t do the same. The Packers still have an opening at linebacker, but the rookie may have fallen at the first preseason hurdle.