French police have questioned four men over a machete attack on Clermont's Aurélien Rougerie, Julien Pierre and Benjamin Kayser, officials said.
The three players were set upon by about 10 armed men as they walked to their hotel in the southern town of Millau in the early hours of Sunday, according to police.
Clermont said that "machetes" and "swords" were used.
"Four men have been detained for questioning. All are aged between 20 and 25 and their detention was expected to be extended for 24 hours on Monday, a deputy prosecutor in charge of the investigation," Cherif Chabbi told AFP.
Chabbi added that three other people were wounded in the attack, some trying to intervene to help the rugby players.
Pierre, who with Rougerie was in the French team that lost the 2011 Rugby World Cup final, required surgery on "deep cuts" to his hip, his club said.
All three were rushed to hospital after the attack.
Rougerie and Kayser were released from hospital Sunday after treatment to cuts to their arms.
They rejoined their team-mates on Monday for a training camp in the Pyrenees. Pierre remained in hospital for an extra day following an operation before heading back to Clermont-Ferrand.
The Clermont players had on a stopover in Millau on their way to a pre-season training camp.
"As they walked back to their hotel overnight Saturday, a group of players was assaulted by a dozen people carrying weapons including machetes, sabres," the club said in a statement.
Police said the incident took place at around 3am after the players went to a nightclub, where they may have been in an argument.
Jean-Marc Lhermet, ASM Clermont's sporting director, told AFP the attack was "unexpected" and "brutal".
"No one was expecting that," he said.
"The evening had gone really well."
Rougerie, 33, is Clermont's captain and has 77 caps for France. Kayser, 29, has played 24 times for France and Pierre, 33, has 27 caps.