Collingwood says it is "devastated" two of its players, Josh Thomas and Lachlan Keeffe, have tested positive to the performance-enhancing drug clenbuterol.

The pair returned a positive test to the A-sample on February 10 and an analysis of the B-sample will take place on April 14.

As clenbuterol is not classified as a specified substance under the AFL Anti-Doping prohibited list, the players have been provisionally suspended.

The Magpies were made aware of the positive test results on Friday and, in consultation with the players, their legal representatives, the AFL, and the AFLPA, decided to release the names to avoid the whole list was caught up in scandal.

Magpies CEO Gary Pert, flanked by director of football Neil Balme, said both Thomas and Keeffe had denied taking the banned drug.

Pert said ASADA had advised him that no other Collingwood players were part of the investigation.

"They looked close to being in shock on Friday. You've got to keep in mind that these are two young men that were at home and had ASADA knock on their door," Pert said.

"Both Neil and myself spoke to them shortly after and the only way I could describe would be they were quite shell-shocked.

PRESS CONFERENCE: As it happened.

"So we weren't pushing the questions that you might calmly sit here thinking we'd be pushing for.

"It was more about supporting the players, making sure they have the right people around them and making sure that they have that (legal) representation.

"I think all parties, including the AFL, handled a really difficult situation well."

listen to ‘Press Conference: Gary Pert and Neil Balme’ on audioBoom

Clenbuterol can be used therapeutically to treat asthma but it is not approved in Australia for human use. It can be legally prescribed by veterinarians in Australia as a muscle relaxant and is often used to treat horses with breathing difficulties.

Clenbuterol is also known to reduce fat and promote weight loss although Balme said he could not see why Keeffe or Thomas would need to take the drug.

"It was disbelief for both of them. They both said 'We haven't done this,'" Balme said

"They're claiming that they're not guilty.

"We know what it is (the drug), which is one of the reasons why we think 'Why would they? How would they?'

"If you look at both of these players, it doesn't make any sense for either of them to use this because they're both quite lean.

Balme and Pert said they would meet with both players in the next couple of days after Thomas and Keeffe met with their legal representatives.

Pert also reiterated the club's earlier statement that it had "conducted a forensic audit of its tightly controlled dietary and nutrition program ... and is completely satisfied the positive results are in no way connected to the program.

Official club statement: Monday, 3.00pm.

"Collingwood is wholly committed to upholding the WADA anti-doping policy and the cause of eradicating performance enhancing drugs from sport."

The Magpies have yet to decide on Keeffe and Thomas' playing futures, preferring to wait until the results of the B-sample are released on April 14.

Keeffe, 24, has played 18 games with the Magpies since making his debut in 2011 while Thomas, 23, overcame a series of injuries to make his debut in round one, 2013. Keeffe suffered a knee injury in 2013 that required a reconstruction.

In a statement, the AFL said the provisional suspension was not an admission of guilt or wrongdoing but a procedural requirement under the AFL Anti-Doping code. 

Keeffe suffered a hamstring injury before the first NAB Challenge game that was only expected to keep him out for a week at the time while Thomas played all three NAB Challenge games.

The latest positive test has come to light the day before the AFL Anti-Doping Tribunal will make its findings in relation to Essendon.

Fremantle's Ryan Crowley is awaiting a tribunal hearing for a positive test he returned during the 2014 season for a specified substance.