Champions Juventus, plus AC Milan, Fiorentina and Lazio could be relegated from Serie A and forced out of European competition if found guilty.

A six-strong panel of judges convened at the Olympic Stadium to try the clubs, plus 26 senior officials, referees and linesmen.

After legal submissions, the tribunal was postponed until Monday.

Lawyers representing five Serie B teams, who hope to be promoted if the accused squads are relegated, want to give evidence.

Judges delayed the case so the representatives of Bologna, Lecce, Treviso, Brescia and Messina could have time to prepare.

The tribunal has been scheduled to run during the remainder of the World Cup in Germany.

Thirteen players in the 23-strong Italian World Cup squad are from the four accused clubs.

Italy face Ukraine on Friday in the quarter-finals and their players say they are focused on the job in hand.

Football-mad Italy has been gripped by the scandal since it broke in May.

It followed the publication of intercepted telephone conversations in which former Juventus general manager Luciano Moggi discussed refereeing appointments with senior Italian Football Federation officials during the 2004-05 season.

 The accused are charged with sporting fraud and unfair conduct, which could lead to the teams being relegated and stripped of their titles and the individuals being either suspended or banned from football.

Other officials on trial include Milan vice president Adriano Galliani, Fiorentina owner Diego Della Valle and Lazio President Claudio Lotito. All have denied wrongdoing.

Chief judge Cesare Ruperto opened the sports trial by reading out the names of the accused to check if they were present.

Moggi did not attend, while Galliani, the highest-ranking Milan official involved, sat in the first row of the improvised courtroom.

Juventus, who have won the Serie A title for the last two seasons, are believed to face the greatest risk of relegation.

Moggi resigned after Juventus claimed their 29th championship in May.

Meanwhile, former Juve midfielder Gianluca Pessotto - who is not implicated in the scandal - is recovering in hospital after falling from a second-floor window at the club's headquarters.

Pessotto, who was appointed team manager in the wake of the scandal, is in a serious but stable condition.

Eight referees face charges, including Massimo de Santis, who had been set to officiate at the World Cup but was pulled out after being drawn into the investigation.

Christian Fraser, the BBC's Rome correspondent, said: "Aside from the four clubs, 26 people will be on trial, including the Juventus former general manager Luciano Moggi, the alleged ringleader of a network set up to influence match officials.

"In return for favours on the pitch, he and his fellow director Antonio Giraudo are accused of wining and dining referees and giving them half-price deals for cars made by Fiat, the company controlled by Juve's owners, the Agnelli family."

The Italian Football Federation (FIGC), which appointed the tribunal, has said it would rule by 9 July - the date of the World Cup final.

Appeals are due to be heard by 20 July, giving the FIGC time before a deadline of 27 July to submit the names of teams to compete in next season's Champions League and Uefa Cup competitions.

If they were relegated, Juventus, AC Milan and Fiorentina would miss the Champions League and Lazio the Uefa Cup.

If they were only docked points next season, they would still be able to compete.

Ruperto, the former head of Italy's Constitutional Court, is presiding over Thursday's session, with only members of the tribunal, the accused and their lawyers in the room.

Reporters will following proceedings in a separate room via closed-circuit television.

The football trial is not a criminal proceeding, but prosecutors in Naples, Rome, Parma and Turin have launched investigations which could lead to criminal charges against some of those accused in the tribunal.