Matu'u, 34, joined from Gloucester in the summer of 2018 and played 30 times for the club, helping Irish return to to the Premiership in 2019.
Naholo, 30, played four times in the 2019-20 but missed all of the current season with a serious knee injury.
Tom Homer and Theo Brophy-Clews have already announced their retirement.
Harry Elrington, Nic Groom, Charlton Kerr, Andrei Mahu and Vladimir Podrezov are also leaving.