Fullback Alex Debniak, who the 49ers signed an undrafted rookie from Stanford, sustained a season-ending torn Achilles tendon on Friday during a workout.

Debniak was waived/injured on Monday. When he cleared waivers on Tuesday, he automatically reverted back to the 49ers and went on injured reserve. He is ineligible to return this season, and he does not count against the 49ers' 90-man roster limit.

On Monday, the 49ers signed fullback Jason Schepler, who played tight end at Northern Illinois, to take Debniak's spot on the roster.

The 49ers converted Debniak (6 foot 2, 240 pounds) to fullback after playing linebacker at Stanford. He played in 38 career games and registered 52 tackles, five sacks and two forced fumbles.

Debniak is the second 49ers player to sustain a torn Achilles in workouts this offseason. On May 21, wide receiver Michael Crabtree was injured when he went in motion and turned upfield. He underwent surgery the following morning. Coach Jim Harbaugh said the team anticipates Crabtree will be able to return late in the season.