Chambers was banned for two years after testing positive for THG

The sprinter, 27, is expected to return to the track at the Norwich Union Grand Prix in Birmingham on 18 February.

But former double Olympic champion Lord Coe said: "It's difficult to be out of the sport competitively for that length of time and to bounce back.

"Dwain must learn the hard way about who his friends in the sport are."

Former 100m European champion Chambers was banned for two years after being found guilty of taking the designer steroid THG.

I saw big potential in him and he got sidetracked by people who did not have his interests at heart Lord Sebastian Coe on Dwain Chambers

World athletics' governing body, the IAAF, also want him to return some of the prize money he won in the year before his positive test in August 2003.

London 2012 chairman Coe, who regards Chambers as a personal friend, said the 27-year-old had been led astray and would find it tough to get back to his old level.

"I hope Dwain has learned to know where his friends in the sport are, and that there are no quick solutions," added Coe, who was speaking at the ticket launch of the 2007 European Athletics Indoor Championships .

"I sincerely hope he can get back to his old level.

"The thing I found saddest about the whole situation, and I'm biased because he's a close friend of mine, is that Dwain was making pretty good progress with (former coach) Micky McFarlane and when Tim Montgomery broke the world record in Paris, Dwain was a pretty close second.