The mercurial scrumhalf limped off the pitch just before the half hour and was replaced by Maxime Lucu, leaving the 7-1 French bench with six forwards.
"I don't have good news. He's got a knee injury and he could not get back onto the field," Galthie said at halftime.
"We're suspecting something serious. He's suffering," he added in the post-match press conference.
"We named the players (who made contact with Dupont), Tadhg Beirne and Andrew Porterto, who should appear before the disciplinary commission.
"We want explanations, so we've named two players. We have to protect our players. There are means, there are rules... There is some kind of anger.
"I'm not going to pass judgement on the quality of the refereeing today," he added when asked about Angus Gardner's decisions.