CHARLOTTE – Vernon Butler was a valuable piece for the Panthers last season as part of a productive rotation, a defensive tackle group again headed by Kawann Short with significant support from fellow starter Star Lotulelei and added support from Kyle Love.

"I like the room the way it is right now. I hope everybody is back," Butler said. "But if that happens, I've got to fill the role and do the job. No doubt, I'll be ready."

The "if" that Butler referred to is the real possibility that Lotulelei has taken his final snap as a Panther. The 2013 first-round pick is set to become an unrestricted free agent when the fifth-year extension on his rookie contract expires at the beginning of the new league year March 14.

If Lotulelei doesn't return, Butler could go from a slowly but steadily developing "luxury pick" (selected late in the first round in 2016) to a player expected to step into a starting role.

"The situation is that if we can get Star taken care of then he'll be there, but if we don't, then we feel comfortable with what Vernon is becoming," head coach Ron Rivera said last week. "We thought Vernon had a good year of growth, and I know he's going to be looking for more opportunities. If he earns them, we'll give them."

To date, though, Butler has been a player better equipped to spell Short than to play alongside him. Butler, like Short, is athletic enough to blow things up by getting vertical, by in effect taking more of a straight line to the quarterback. Lotulelei is more of a space-eater, occupying blockers horizontally across the line to free things up for players like Short and Butler to penetrate.

Eric Washington, shortly after being elevated from defensive line coach to coordinator a month ago, said he's not looking to replace Lotulelei with Butler, but someone will line up beside Short in Week 1.

Size is on Butler's side. At 6-foot-4, 330 pounds, he's actually two inches taller and 15 pounds heavier than Lotulelei.

"He's a big, athletic guy who is explosive and quick – a lot in the mold of KK," Rivera said. "But he can (play like Lotulelei) because of his size and his strength."

Butler's stats in 2017 didn't scream that he's ready for a larger role, but proportionally he was statistically as productive as Lotulelei (though, admittedly, stats don't come close to telling the whole story at defensive tackle).

While playing about 60 percent of the snaps, Lotulelei recorded 26 tackles, 11 quarterback pressures and 1.5 sacks last season. Butler, playing roughly half of Lotulelei's total snaps, recorded 14 tackles and 11 quarterback pressures.

"Since I've gotten here, I've watched those guys and have been doing what they do. That's changed my whole game," said Butler, who gave equal credit to Washington. "I was out there giving my all every day, every game, but I want to be more consistent next year."

To that end, Butler is attacking the offseason. Planning to train at times in Atlanta and Dallas, Butler said he wanted to shed a few pounds and work hard on fundamentals in anticipation of what could happen next season.

"I'm going to hit hard, get in the lab and get ready. I'll come back in shape and be ready," Butler said. "It was fun coming to work every day, and I could see the difference in my game from this year to last year.

"I'll just keep working hard, and next year will be a big year."