The 20-year-old Nwakali, who first joined Arsenal in 2016, played the 2016-17 season on loan for the Dutch second tier "Eerste Divisie" club MVV Maastricht, making 34 appearances and scoring three times, reports Efe.
Last season, Nwakali played again on loan, this time for the first tier Dutch Premier "Eredivisie" club VVV Venlo in 2017, making 11 appearances and scoring once.
Nwakali's transfer to Porto is pending the completion of regulatory processes Arsenal said on its official website.