Koscielny gutted for Arsenal pal Sagna over Euros
Koscielny knows the injury is a huge blow for his club-mate but insists his compatriot will return from his setback even stronger.
"Bac is a very nice guy off the pitch and he has been very professional because it is the second time he has been injured like this," Koscielny told Arsenal Player. "I think it is really hard for him because he trained hard to come back and help the team.
"So for him not to be in the French squad is disappointing. But I know Bac, he will come back stronger and next season he will be very important for us."