The exodus of top Clemson Tigers underclassmen has begun, with first-round prospect Dexter Lawrence headlining a group of three players to declare for the NFL draft on Wednesday.

Cornerback Trayvon Mullen and linebacker Tre Lamar join Lawrence in leaving school early.

Lawrence, a 6-foot-5, 340-pound defensive tackle, ranks No. 14 on Mel Kiper's Big Board of the top 25 draft prospects. A starter since his true freshman season, Lawrence has been a force in the interior of the Tigers' vaunted defensive line, earning All-ACC honors twice.

Lawrence's departure means Clemson loses all four of its starting defensive linemen, as Clelin Ferrell, Christian Wilkins and Austin Bryant are all seniors.

But there will be some tough questions for Lawrence to answer during the draft vetting process, as he was suspended for the College Football Playoff after testing positive for a banned substance in December.

During media day for the Goodyear Cotton Bowl, Lawrence said he didn't know how the banned substance appeared in the drug test he took.

"I'm not the type of guy to do a selfish act like that," he told reporters.

Thank You, Clemson Family 🐅 pic.twitter.com/ZdDXiRh9QF — Trayvon Mullen Jr (@MullenIsland1) January 9, 2019

Mullen, rated Kiper's No. 5-rated cornerback, started 14 games this season for the national champions and had a big performance in the championship game against Alabama, with six tackles, an interception and forced fumble. He was a second-team All-ACC selection.

Lamar, rated Kiper's No. 9 inside linebacker prospect, finished second on the team with 85 tackles and also was a second-team All-ACC selection.

Mullen and Lamar were indispensable parts of a Clemson defense that ranked No. 5 in the nation and shut down its two playoff opponents, Notre Dame and Alabama, holding them to a combined 19 points.