ARLINGTON, Texas -- Clemson will officially be without three players, including starting defensive lineman Dexter Lawrence, for the Tigers' College Football Playoff semifinal at the Goodyear Cotton Bowl Classic after B samples of NCAA drug tests also showed trace amounts of a banned substance.

"This evening, Clemson Athletics received confirmation from the NCAA of suspensions of tight end Braden Galloway, offensive lineman Zach Giella and defensive tackle Dexter Lawrence, all three of whom will be unavailable for Saturday's game against Notre Dame," Clemson director of athletics Dan Radakovich said in a statement. "The athletic department will have no further comments on this matter this evening as it considers all of our options, including appeals."

The Tigers had been preparing for its Goodyear Cotton Bowl Classic matchup with Notre Dame assuming Lawrence would not play. The junior, who is widely projected as a future first-round NFL draft pick, has not practiced with the team since Clemson learned of the initial positive test last week.

Lawrence was excused from Thursday's media day but asked to talk with reporters anyway. He said he had no idea how the substance got into his system and denied ever taking performance-enhancing drugs.

"We get tested regularly and we know not to do anything stupid or selfish like that," Lawrence said. "That's why this is such a shock."

Lawrence, along with freshman Galloway and junior Giella, now faces a suspension of up to one year, pending appeal. That probably means the end of Lawrence's college career, although he said Thursday he had not made a final decision about his NFL prospects.

"I'm just in the moment trying to help the team the best I can and be the leader I've been all year," he said. "Just right now I'm doing it behind the whistle."

Lawrence has been working with the coaching staff to prepare Albert Huggins and Nyles Pinckney for a bigger role in Saturday's game.

Clemson starter Dexter Lawrence denied ever taking performance-enhancing drugs. "We get tested regularly and we know not to do anything stupid or selfish like that," he said Thursday. Brett Carlsen/Getty Images

Meanwhile, coach Dabo Swinney said the school was investigating potential ways the substance could have been consumed without knowledge by the suspended players, including looking at supplements, treatment including its salt-water float pool and aspects of treatment Lawrence received following offseason surgery.

The substance, ostarine, is not approved by the Food and Drug Administration and is not legally for sale in the United States. There have been instances, however, of the drug being used in supplements without being included on the label. Clemson players said this week that the school closely monitors what supplements are made available to players, and all players have a list of what has been approved by the training staff.

If this is the end of Lawrence's career at Clemson, he'll finish with 133 tackles, including 19.5 for a loss, and 10.5 sacks.

"I didn't want my last game to be Pitt [in the ACC championship]," Lawrence said Thursday. "I wanted my last game to be the closer. That's what we'd been fighting for each game. I wouldn't wish this on anybody."