Gelez, 24, was named first-choice stand-off three weeks ago after usual goalkicker Gerald Merceron missed two penalties and one conversion in Les Bleus' 25-17 defeat to England in their tournament opener on February 15.
Against Scotland the young Agen player vindicated coach Bernard Laporte's decision by scoring 18 of a possible 20 points during the 38-3 victory at the Stade de France.
But during that clash, captain and scrum-half Fabien Galthie injured his right shoulder and was forced to pull out of their match at Lansdowne Road, leaving a vacancy filled by Yachvili, the 22-year-old Biarritz hope.
Many have questioned whether such an inexperienced pair are sufficiently prepared for such a highly-charged encounter but Gelez is not worried even though he has never before played with Yachvili.
"I am not worried at all," Gelez said. "If they (Laporte and team manager Jo Maso) decided to pair us it is because they think we can make the team play well.
"It is true that we don't know each other, but we will try to do things simply, communicate a lot and it should be fine.
"We have been playing together with the French team for the past few weeks so everything is not totally new.
"However a half-back combination cannot become perfect within one week, we will need to work a lot."