Sir Mo Farah says he is happy for his old samples to be retested at any time.

The World Anti-Doping Agency is expected to retest the samples of some athletes who belonged to Alberto Salazar's Nike Oregon Project (NOP).

The investigation comes after the American coach was banned for four years in 2019 for violations of the anti-doping rules following a probe by the US Anti-Doping Agency.

UK Anti-Doping chief executive Nicole Sapstead said last week that it would need to see "credible evidence" that there was a justification to hand over samples to any other agency.

British athlete Farah, 36, trained as part of the now-defunct NOP between 2010 and 2017 but has never tested positive at any stage in his career.

On Tuesday he tweeted to say he was more than happy if his existing samples were looked at again.

"I've seen reports of my name in connection to UKAD and WADA about sample retesting," he wrote.

"Just to be clear, I was not consulted about this and as I've said many times, I am happy for any anti-doping body to test any of my previous samples anytime."

Sapstead told The Guardian last week: "We supported USADA in their investigation into the Nike Oregon Project.

"There has never been any ill-feeling or lack of willingness or assistance on our part. But when you open a sample up, every time you freeze it and thaw it and freeze it again, you are degrading the sample. I was simply saying to USADA: 'You need to be able to give me credible evidence about what it is you want to look for, rather than this just being a trawling expedition'."

Farah said in a BBC interview earlier this month that he would have severed his ties to Salazar sooner had the evidence of wrongdoing been there.

"Had I had known the news, what Salazar did, it's taken four years, had I known that sooner I would have been the first one out," he said.

"That's the bit that's kind of annoying, I wish I'd known quicker."

Salazar has appealed against his sanction to the Court of Arbitration for Sport.