Nicholson, the former West Bromwich Albion defender, had his suspension from the game lifted by a Football Association disciplinary commission following a ban imposed in February for failing to supply a random drugs test. The three-man commission reached their decision after hearing progress reports on Nicholson's rehabilitation.
Brendon Batson, the Professional Footballers' Association deputy chief executive, believes Nicholson could play a vital role in the union's anti-drug programme.
"Anybody with a similar problem who wants to discuss it with someone can talk to Shane, who has been through it and can speak with some authority," he said.
Nicholson is currently training with Second Division Chesterfield and there has already been "interest" from other clubs.
Keith Gillespie, the Newcastle winger, has scotched reports that he is set to retire and insists he will be back in action soon.
"They are totally untrue," he said. "I've had the OK from both physios, I've seen a couple of specialists and hopefully I'll be resuming training on Monday."
The Chelsea player-manager, Gianluca Vialli, has confirmed he will sue Zdenek Zeman after the Roma coach made a thinly-disguised claim that he took illegal performance-enhancing drugs. Zeman made the comments in an Italian magazine last week. "If someone has made a mistake then they must pay for it, but it will not be me," Vialli said.
Tottenham have turned down an undisclosed bid for Steffen Iversen from PSV Eindhoven.