The Ligue 1 club has accepted offers from both clubs for Magalhaes, but the Brazilian defender will decide his next team.
“I think he has narrowed it down. Arsenal are [of] high interest to him. Napoli is [of] high interest to him.
“I don’t think I am giving up too much if I tell you that choice is going to be made between today or tomorrow,” he told talkSPORT.
The 22-year-old is believed to have chosen the Gunners and will undergo medicals with the Premier League side.
When asked specifically if Arsenal was the player’s first choice, Lopez said: “I don’t want to say that and I don’t want to speak for the player.”