Clemson defensive tackle Dexter Lawrence says he doesn't know how a banned substance appeared in a drug test he took this month, and the Tigers are hoping to learn the results of a secondary test by the end of the day Thursday.

Lawrence said he was shocked when head coach Dabo Swinney informed him last week that he had tested positive for a substance that would leave him ineligible to play in the College Football Playoff.

"I'm not the type of guy to do a selfish act like that," Lawrence said Thursday morning at AT&T Stadium. "I have too much pride. I love this team and my family too much to put a substance like that in my body. I don't know where it came from. I don't know how it got there. I was raised different. If I did do it, I'd own up to it. All I can say is I honestly don't know what happened, where it came from."

Lawrence thinks his positive test could be the result of something that entered his body in an energy drink or even hair gel.

Lawrence was one of three Clemson players flagged for having small amounts of a muscle growth substance called ostarine show up in a recent drug test. Lawrence, backup offensive lineman Zach Giella and freshman tight end Braden Galloway will not be able to play against No. 3 Notre Dame in the Goodyear Cotton Bowl Classic this Saturday unless they are cleared of wrongdoing by the secondary test.

Swinney said he has "no clue" if those three players will be available for the semifinal game, but Clemson is preparing for the game as if they will not be able to play.

"The only thing I know is these guys have not intentionally done anything," Swinney said Thursday morning.

Swinney said he learned about the test results last Thursday and wanted to be as transparent as possible because he believes his players didn't intentionally take a banned substance. He said he has treated their absence like an injury and moved his focus to preparing for Notre Dame as they wait to learn more.

The facility testing the backup samples is located somewhere near Los Angeles, according to Swinney, and it was too early to expect to hear from them when he met with reporters at 8 a.m. CT in Texas.

Swinney said having Lawrence on the field against Notre Dame would be "a cherry on top" to a defensive line that is considered one of the deepest and most talented units in college football. If Lawrence is unable to play, senior Albert Huggins is likely to take his place in the starting lineup. Huggins averaged more than 20 snaps per game on the defensive line during the 2018 season.

"Huggins is a co-starter for us anyway. I don't have any doubt that he'll step in and do a great job for us," Swinney said.

Lawrence said he is "at peace" with the uncertainty heading into Saturday's game. He said he was in Texas to support his teammates and to try to be a leader if the secondary sample doesn't clear him to play.