The news might help ease the tense atmosphere surrounding the France camp ahead of the June 11-July 11 tournament.
"As the case stands now, it is not expected Ribery will be summoned by the judge to be possibly placed under official investigation before the start of the competition," the judicial source said, declining to be named.
The source added that another French international, Real Madrid striker Karim Benzema, who also faces questioning in the same case, would not be heard before the World Cup.
Junior Sports Minister Rama Yade said on Thursday that any player placed under investigation should not represent France.
"The French shirt is sacred and cannot be worn by somebody who is under official investigation," she told Canal+ television late on Thursday.
France playmaker Ribery and fellow international Sydney Govou were questioned earlier in April as witnesses by police investigating a prostitution network.
French media have said the players were clients of a nightclub in Paris's posh Champs-Elysees district that allegedly featured escort girls.
Ribery's lawyer has said her client was only questioned about his ties with the leader of an escort girls network and the player himself has made no comment about the affair.
Govou's lawyer and Benzema's agent deny that their clients had ever been to the nightclub in question.
NEW TWIST
On Thursday, the scandal, which has gripped France, took a new twist after a young woman involved in the case gave a lengthy interview to Paris Match magazine about the scandal.
She said Ribery had invited her to Munich in April 2009 to celebrate his 26th birthday in a luxury hotel, adding that he had paid her for three encounters last year.
Zahia, who turned 18 in February, confirmed widespread reports in the French press that she was underage when she met Ribery, but added that she had not informed him about her age.
There was no immediate comment from Ribery's entourage.
Ribery, usually energetic on the pitch and unassuming off it, is probably the most popular player in the squad, since Zinedine Zidane, who retired after his infamous headbutt in the defeat by Italy on penalties in the 2006 World Cup final.
But he has had a wretched few weeks, hounded by the media over the scandal, suffering injury and then getting sent off earlier this month during Bayern Munich's Champions League semi-final.
UEFA have since given him a three-match ban which means he will miss the final against Inter Milan. Bayern have appealed and UEFA said on Friday that the hearing would take place on May 5.
Given his various woes, some sports commentators in France have questioned whether French coach Raymond Domenech will even select him for the World Cup.
France's Immigration Minister Eric Besson said on Friday the case was taking "undue importance" and that Ribery was entitled to the presumption of innocence like any citizen.
