MADRID, July 5 (Reuters) - Joan Laporta's five-year reign as Barcelona president could be nearing its end if club members turn out in large enough numbers to vote against him in Sunday's motion of confidence. The referendum has been forced by club member Oriol Giralt, who gathered enough signatures to support his motion criticising Laporta's administration of the club. To be successful, the vote against Laporta will need to have the support of over two-thirds of voters with a minimum turnout of 10 percent of members entitled to take part. If that happens, the opposition will be able to force a presidential election in which Laporta's former aide Sandro Rosell has said he will stand. Rosell was responsible for bringing Ronaldinho and Deco to the club when he was Laporta's vice-president, before resigning in 2005, saying he was unhappy with his boss's domineering style. Laporta presided over the club when it won back-to-back league titles and the Champions League but has been heavily criticised for his running of the club over the past two years. Fans staged several protests calling for his resignation towards the end of last season after the team failed to win any silverware for a second successive year. The club responded by sacking coach Frank Rijkaard and appointing ex-captain and Nou Camp favourite Pep Guardiola as his replacement. In an attempt to revitalise the squad, they have signed Brazil fullback Daniel Alves and Mali midfielder Seydou Keita from Sevilla, former youth team player Gerard Pique from Manchester United and Uruguay centre back Martin Caceres from Recreativo Huelva. Guardiola also made it clear that leading players Ronaldinho and Samuel Eto'o did not feature in his plans for next season.