The Financial Services Authority (FSA) has issued a warning to all listed football clubs to stick to stock market rules.
Beckham was the subject of furious transfer speculation last season
The watchdog sent out a letter to the nine listed clubs, which include Manchester United and Chelsea, reminding them that any "price sensitive information" must be made public.
It added that the letter was simply to remind clubs of the rules on sensitive news, and that no one club was being targeted.
Spokesman David Eacott said: "Football clubs need to keep their supporters informed but they should not forget that they are obliged to tell shareholders of any move in the transfer market."
Ken Rushton, Director of Listing, told the clubs: "The UK Listing Authority recognises that at certain times of year, particularly during open transfer windows, the likelihood of price sensitive information increases, as does press speculation in relation to such developments."
He added clubs must take action to ensure any such developments, must be released "without delay".
UK listed football clubs
Heart of Midlothian
Such news would include "a transfer deal with short or long term financial consequences that are material to a club's prospects".
Mr Rushton also warned firms should be prepared for any leaks and be ready to confirm or deny them through the market's Regulatory Information Service.
Third parties involved in negotiations should also be told to stick to FSA rules, he said.
Mr Rushton ended the letter: "I would also like to take this opportunity to remind you that sanctions for failure to comply with the Listing Rules include public censures and unlimited fines."
The news comes as Chelsea FC's takeover is the subject of two investigations by the watchdog.
One inquiry centres on the ownership of the club prior to its recent takeover by Russian billionaire Roman Abramovich.
The FSA is probing Roman Abramovich's takeover of Chelsea
The FSA said it had been tipped off that the information it had on the number of Chelsea shares owned by some investors may have been inaccurate and that "as a consequence the market may have been misled as to the true ownership of Chelsea Village plc".
Meanwhile, it is also probing movements in Chelsea's share price in the days before Mr Abramovich's takeover was announced.
Shares in Chelsea Village soared by 40% between 13 June and 1 July, the day the Abramovich deal was unveiled.
A surge in share prices ahead of a takeover can arouse suspicions of illegal insider trading, although there is no suggestion of wrongdoing by the main parties in the Chelsea takeover.