The striker arrived in the summer from Bordeaux.
"He has improved already," Sagna said. "When he arrived here he was a bit, well, not scared, but he certainly needed time to settle. That's happened already and he has found his feet.
"It's so important for the team to have a player like him up front. He can keep the ball well and he just wants to play, give his best and work for the team. He'll get better results with each game he plays. For the team he will be very important. He will become a great player for Arsenal."