The Jaguars confirmed the severity of the injury, which was initially reported by ESPN, on Friday. Fowler will undergo surgery in the coming weeks and is expected to miss the entire 2015 season.
The 6-foot-3, 260-pound defensive end went down during a drill when his left leg buckled as he rushed the passer. He was helped off the field by trainers.
Fowler was drafted third overall last week after racking up 14 1/2 sacks in three seasons at Florida.
Dolphins sign entire draft class
The Miami Dolphins have signed wide receiver DeVante Parker, defensive tackle Jordan Phillips, offensive lineman Jamil Douglas, cornerback Bobby McCain, running back Jay Ajayi, safety Cedric Thompson and cornerback Tony Lippett.
Parker, the 14th overall selection in the 2015 NFL Draft out of Louisville, played in 42 career games with 18 starts while with the Cardinals and recorded 156 receptions for 2,775 yards and 33 touchdowns. His 33 touchdowns tied a school record and he earned second-team All-ACC honors as a senior in 2014 despite playing in only six games.
Phillips was Miami's second-round selection (52nd overall) in last weekend's draft. He played in 28 career games with 17 starts at Oklahoma and recorded 57 tackles, 3 1/2 sacks, two passes defensed and one fumble recovery.