Britain's Laura Muir has started working with a coach from the controversial Nike Oregon Project.
The project is led by Mo Farah's former coach Alberto Salazar, who is being probed by the US Anti-Doping Agency.
Scottish middle distance runner Muir, 24, has told fans "not to worry" after linking up with coach David McHenry.
Muir has previously said she does not speak to rival Genzebe Dibaba following links to a coach arrested as part of an anti-doping investigation.
Dibaba's coach Jama Aden denies any doping offences, while the Ethiopian world champion has always maintained she is clean.
Muir, who won bronze and silver at the World Indoor Championships in March, will continue to be coached by Andy Young.
"Don't worry guys Andy is still my only coach," said Muir.
"I am planning on starting working with one of Nike's (and the world's) top strength and conditioning experts, although for now it's by video clips and I haven't progressed past the floor exercises with the rubber band."
BBC sports editor Dan Roan
Muir's decision to work with McHenry may make sense from a pure athletics perspective, but in terms of PR, it will raise eyebrows. Firstly because of his close ties with Alberto Salazar's Nike Oregon Project, where McHenry is lead strength and conditioning coach.
Salazar has always denied wrongdoing, but ever since allegations from former Nike Oregon Project athletes and employees to BBC's Panorama programme in 2015 he has been under investigation by Usada.
So any kind of association with him inevitably comes under scrutiny, even if Muir has now tried to downplay her plan to work with McHenry, after it was revealed by the Daily Mail.
Secondly, Muir said last month that she will not speak to her great Ethiopian rival Genzebe Dibaba over her links to Jama Aden - another coach under investigation by anti-doping authorities - leaving her open to suggestions of hypocrisy.
There is no suggestion of any wrongdoing by Muir, but UK Athletics' willingness to sanction such a move by the golden girl of the sport will surprise some observers.