The 22-year-old got the nod ahead of South African-born centreBrian Liebenberg, who had been thought of as a possible replacement forMichalak.
"We talked it over with Liebenberg," said France coachBernard Laporte. "However we felt he wasn't ready for it. He explained that he hasn't played fly-half for two years atStade Francais," added Laporte.
Laporte revealed that 21-year-old Michalak could have played ifthey had given him an injection to relieve the pain.
"However we thought in the best interests of the player andhis club that we couldn't do such a thing," said Laporte.
Peyrelongue, 22, was due to play for the France A side this weekand will form a relatively inexperienced halfback partnership - the 19th under Laporte's five year stewardship - with Jean-Baptiste Elissalde, whowon just his fifth cap in the 35-17 defeat of Ireland last Saturday.
Before the Ireland match, Elissalde had only made four briefappearances as a replacement and he will have extra duties on Saturday as he willhave to do all the kicking for goal as Peyrelongue is not a specialist.
Laporte, though, had no qualms about pitching the Biarritzfly-half into the fray against the weakest team in the tournament, who werethrashed 50-9 by
"Peyrelongue is a very good player," said the39-year-old. "The only small problem is that he can't kick for goal. However he is good both in attack and in defence and he hasprogressed a lot in his kicking out of hand," added Laporte, who wasespecially vexed by Michalak's positional kicking against the Irish.
Peyrelongue burst into the spotlight in 2002 when Biarritz won theFrench championship and is a former French Under-21 international.
Both of the players who made their debuts against Ireland --hooker William Servat and lock Pascal Pape, who scored a try, retained their placesahead of the vastly more experienced Yannick Bru and David Auradou.
France: Nicolas Brusque (Biarritz); Vincent Clerc (Toulouse), YannickJauzion (Toulouse), Damien Traille (Pau), Christophe Dominici (StadeFrancais); Julien Peyrelongue (Biarritz), Jean-Baptiste Elissalde (Toulouse); Imanol Harinordoquy (Pau), Olivier Magne (Montferrand), Serge Betsen(Biarritz), Pascal Pape (Bourgoin), Fabien Pelous (Toulouse, capt), Pieter DeVilliers (Stade Francais), William Servat (Toulouse), Sylvain Marconnet (StadeFrancais) Replacements: Yannick Bru (Toulouse), Jean-Jacques Crenca (Agen),David Auradou (Stade Francais), Thomas Lievremont (Biarritz), DimitriYachvili (Biarritz), Brian Liebenberg (Stade Francais), Pepito Elhorga (Agen)