The UK's advertising watchdog has banned a Nike Twitter campaign in its original form.
The ruling follows tweets by Manchester United footballer Wayne Rooney and his Arsenal rival Jack Wilshere, posted at the request of the sportswear firm.
The Advertising Standards Authority said that the messages did not make clear they were "identifiable as marketing communications".
It marks the first time the ASA has acted against a Twitter-based campaign.
Followers of Wayne Rooney might have mistaken his tweet about Nike in January as a genuine expression of the footballer's thoughts, the ASA suggested. In fact, the tweet was composed by "a member of the Nike marketing team".