Jake Ryan enjoyed a breakout 2017 season, but the fourth-year linebacker may not have a chance to build on it. At least, not right away.

While it’s not certain just yet, the Packers fear one of their starting inside linebackers suffered a “significant and potentially season-ending” right knee injury, Rob Demovsky of ESPN.com reports. Pro Football Focus’ No. 19 overall linebacker last season, Ryan suffered this setback during an 11-on-11 drill at Packers practice Monday.

The former fourth-round pick, who’s entering a contract year, has started 27 games with Green Bay since his rookie season. If it’s determined Ryan will miss time, Demovsky notes third-round rookie Oren Burks could be thrust into action alongside Blake Martinez. The Packers have also been impressed with rookie UDFA Greer Martini, per Demovsky.

Ryan played 506 snaps last season, and although his 79 tackles were well off Martinez’s league-leading 142, PFF preferred his coverage to Martinez’s work as Green Bay’s other primary linebacker.

Safety Kentrell Brice, whom Demovsky writes may be the leading candidate to replace Morgan Burnett, was also carted away from practice Monday. Brice was running with Green Bay’s first-string defense. Josh Jones, a 2017 second-round pick, replaced Brice with the starting defense.