The agency's Glasgow office was until recently working with Lithuanian businessman Vladimir Romanov, the outspoken owner of Scottish Premier League football club Heart of Midlothian (Hearts).
Weber Shandwick director Charlie Mann said the agency had resigned the account after acting as Romanov's spokespeople for four years.
'The UK media are more open than Romanov was used to,' said Mann. 'He had a fractious relationship with the Scottish press and when he said he didn't want to communicate with the press anymore, there was no point in continuing to work with him.'
Romanov's PR activity will now be handled by the club's internal PR team.
Romanov is well known in the press for his controversial comments. In 2006, Hearts was fined £10,000 by the Scottish Football Association after Romanov's criticism of match officials. In another spat with the press last year, he insisted he was misquoted by a newspaper that suggested he accused the Old Firm of 'buying off' players and referees.