Sources told ESPN's Mark Schlabach that the No. 2 Tigers don't anticipate having all three players for Saturday's College Football Playoff semifinal against No. 3 Notre Dame (4 p.m., ESPN/ESPNApp) at AT&T Stadium in Arlington, Texas.
"We do have an issue that we're dealing with," Swinney told reporters. "And, you know, I think that the best thing is to just be transparent in that."
Swinney said he expects B-sample test results, which would determine the players' eligibility for the game, to be available Wednesday or Thursday. The B-samples are secondary tests to weed out false positives.
"We're just kind of at the mercy of the process," Swinney said. "And then there's an appeal after that, but that doesn't really help with this game.
"... And so we'll deal with it accordingly, hope for the best, hope that the B-sample will come back and they'll be cleared to play. But if not, we treat it as an injury. We've got to get ready to move forward. And our goal has not changed, just to play the best four quarters of the season."
If the players are not cleared after the appeal, the undergraduate players will be subject to a one-year suspension.
Swinney said the players said they have no clue how ostarine got into their samples. Ostarine is a product used to promote muscle growth. It is on the World Anti-Doping Agency's list of prohibited substances.
"This particular substance can come from anything," Swinney said. "And these three players have no clue -- in fact, they thought it was a joke when I called them. They have no clue how this has gotten in their system. It could come from hair products. It could come from a cream. It could come from protein. It could come from a product that you order or buy online that you think there's nothing wrong with it. It could be anything. Literally, it could be a drink -- something in a drink.
"... We're going to do everything we can to figure out if it is in the system. Heck, I don't know. I mean, who's to say that it is there? I mean, that's what we're being told, but there's -- they all will have legal representation, and there will be a process to go through to find out."
Lawrence is a 340-pound mainstay in the middle of Clemson's defensive line, widely considered to be one of the nation's most talented groups. He was first-team All-ACC and is the No. 23 prospect on Mel Kiper's Big Board.
Giella has played sparingly in a reserve role this season. Galloway caught five passes in a backup role during the 2018 regular season.
"I think it's important, very important, that the message is accurate and that the truth is told because these are three great young men, three great young men, that I believe in and that I know, without a doubt, have not intentionally done anything to jeopardize their opportunity or this team," Swinney said.