The US Anti Doping Agency has launched an investigation into the activities of the American athletics manager, Mark Block, who is currently serving a ten year suspension for his involvement in doping.

Block was implicated in the infamous BALCO scandal and provided his wife, sprinter Zhanna Pintusevich-Block, with Tetrahydrogestrinone otherwise known as "The Clear" the undetectable steroid compound. Pintusevich-Block famously defeated the now disgraced Marion Jones to win the 2001 IAAF World Championships 100m title.

As part of his punishment Block is forbidden to represent track and field athletes and started working as a real estate agent in Florida. The ban was handed down in March 2011. However, he has been seen in the company of American world champions Carmelita Jeter (100m) and Jason Richardson (110m hurdles) at competitions around the world leaving observers wondering if he is practicing athlete management illegally behind the scenes.

There is no suggestion however that he is practising athlete management with Jeter and Richardson, neither of whom have ever failed a drug test or had any doping allegations made against them.

Jeter deflected questions on the subject during the US Olympic trials telling a press conference that her agent is Chris Layne, formerly Block's partner at Tennessee based Total Sports US.

Reached in London where he is attending the Olympics this week Layne refused comment saying only "I am not going to talk about it. It's a non issue."

USADA has received complaints that Block has maintained contact with athletes which prompted their investigation. Compounding the issue is the fact that Block was photographed exiting the Nike VIP box at the US Olympic trials in Eugene, Oregon. Having a persona non grata being entertained by one of the USA Track and Field's biggest sponsors is clearly an embarrassment to the sport and to the company.

Jill Geer, Director of Communications for USATF, declined to comment citing the ongoing USADA investigation. Meanwhile, USADA spokesperson, Annie Skinner, chose her words carefully.

"We are definitely aware of this and it's not something we take lightly," Skinner said. "We will continue to take due diligence. USATF have pieces in place to ensure he is not credentialed. But they can't prevent people from attending meets.

"But he is not allowed to work as an athlete representative. He doesn't have authority to do that. He didn't receive credentials at the US Olympic trials. There is an investigation going on."

Until his suspension Block was a member of the Association of Athletics Managers, a collection of 35 of the world's leading agents, who work with the IAAF and meeting directors on behalf of the athletes. He voluntarily resigned from the AAM. Contacted at the London Olympics several managers had strong opinions on the matter though none would speak unless their anonymity was guaranteed.

"It's a very disappointing and uncomfortable situation," said one. "I don't think we can tell someone they can't go to track meet. Does Nike deal him with for Jeter? I don't know.

"Meet directors are only supposed to deal with authorised managers. If he was still a manager we could do something about it. We are not a police authority. What are the implications for athletes for using someone who is banned? What about using people who are not members of AAM? Nothing.

"We, in this sport, ban somebody for ten years. What does that mean? The guy banned doesn't know. Is he forbidden from speaking to former clients? Can he go to track meets at his alma mater? To high school track meets?"

Another European based agent echoed the frustration fellow managers feel knowing that the sanctions have, until now, not been policed.

"I can tell you there are many individual opinions about this, strong opinions," he told the Sunday Herald. "I think most don't want to be quoted on this.

"If anything is upsetting it's that there's no teeth to the sanction. It's not my problem it's IAAF, USATF and USADA, those three organisations. Mark Block is a nice guy who made a mistake but he must take punishment."

Authorised agents normally negotiate appearance fees with meet directors on behalf of their clients. They receive a percentage of the fees. Rajne Soderberg, president of Euro Meetings, a group of the most prestigious European athletics meeting promoters, says his organisation is watching the outcome of the USADA investigation. Like many observers he wonders whose duty it is to police the ban.

"We have not discussed his case in particular but, of course, I assume that all the organisers do follow the regulations that are set," said Soderberg. "He's banned from athletics competitions and dealing with the sport. Of course, he cannot come to a meeting as an accredited manager. If he is there it might be that he's buying his own ticket, his own hotel room, at his own expense.

"He has been seen. He was actually in Stockholm when I did the meet last year. I saw him on the street. But he was not accredited."

Soderberg says the one day meetings don't usually use photo identification and an athlete can ask for accreditation for managers, coaches and physiotherapists. There is no control over who receives these.