Dwain Chambers won the 60m indoor European title earlier this month
The world governing body for athletics, the IAAF, says it is "very surprised" that British sprinter Dwain Chambers has renewed links with Victor Conte.
Conte is the man behind the doping scandal that led to Chambers' two-year ban from the sport in 2003.
Chambers is using a hi-tech breathing device to boost his oxygen capacity under the supervision of Conte.
"We're very surprised that he's still associating with people like Mr Conte," said an IAAF statement.
"And if he's looking forward to a career and claiming that he's doing that in all legality, it's probably wise to disassociate yourself with people with a reputation for being involved in doping in sport."
Conte served a four-month prison sentence for his central role in the wide-ranging Balco (Bay Area Laboratory Co-Operative) scandal that enveloped several top-level athletes.
Chambers tested positive for he banned substance THG in 2003 and served a two-year suspension.
The 30-year-old's return to athletics has been dogged by controversy and the sprinter has been largely frozen out of the sport since returning from his ban.
As a result he has found it almost impossible to repay the money he earned while taking illegal performance-enhancing substances in 2002 and 2003.
He did, however, claim the European indoor 60m title earlier in March, and has made no secret of his continued friendship with Conte, who has defended his latest link-up with Chambers.
"For educational purposes, I recently provided some legal performance enhancement consultation to Dwain Chambers," said Conte in a statement.
"This information involves strictly legal nutritional supplements and methods. The assumption that Dwain's recent association with me means he is using drugs is ignorant.
News that Balco kingpin Conte is still advising Chambers will concern many
"If anything, our association suggests that he is not using drugs because it only causes him additional scrutiny."
The oxygen device Chambers has been using simulates the effect of training at high altitude. It enables him to breath low and high oxygen through a hypoxicator to boost his red blood cell count.
"This allows me to have a deeper training load," said Chambers.
"I suffer less lactic acid, delivering more oxygen to the muscles.
"It's a shame we didn't know this five years ago."
The apparatus is legal under World Anti-Doping Agency rules.
"This is the wave of the future," Conte said.
"Everyone used to think (simulated altitude training) was all about endurance athletes. No one thought of applying this to explosive sprinting."
Former 100m world record holder and Olympic gold medallist Donovan Bailey believes Chambers should stay clear of linking up with Conte.
"Victor has a bad reputation because of what happened between him and Dwain in the past," said Bailey.
"It is Dwain's responsibility to train clean and compete at the highest level.
"If he can get good advice from someone and Victor wouldn't be my first choice for him, and he's clean, then that's a good thing."