JACKSONVILLE, Fla. -- Jacksonville Jaguars linebacker James Onwualu will miss the season because of a knee injury, leaving the team pretty thin at that position as the preseason begins on Thursday.

Coach Doug Marrone called the injury that Onwualu sustained on Monday during joint practices with the Baltimore Ravens significant, but declined to elaborate on its exact nature. Onwualu was listed as the co-starter with Leon Jacobs at strongside linebacker on the team's first unofficial depth chart.

"It's something that was a non-contact injury for the guys that have seen it and those are tough," Marrone said. "And he's worked his butt off, and worked really hard, and I saw him yesterday afterwards and it's just a tough situation. You thank the player for everything he put in, but you kind of know what the road looks like ahead, which is always a tough road for anyone that has an injury."

The Jaguars claimed Onwualu off waivers on April 30 after he was cut by the San Francisco 49ers. He signed as an undrafted rookie with the Los Angeles Chargers in 2017 and played in 10 games; he appeared in five games for the 49ers last season. He has eight special-teams tackles and one forced fumble in his career.

Onwualu is the second Jaguars linebacker to get hurt in the past week. Quincy Williams, one of the team's two third-round picks, was diagnosed with meniscus damage in his right knee last Thursday. The team said he would miss four to six weeks but Marrone said he believes Williams, the leading candidate to replace Telvin Smith, will return in time for the season opener.