Mateo, who can play across the back-row and at stand-off, broke into the NRL with Parrmatta in 2004.
He had short spell with London in 2005 and has also had a four-year spell with the New Zealand Warriors.
Mateo joined the Sea Eagles in 2015 but has rarely featured for them.
A highly-skilled player, the lock could add some spark to Salford’s pack for the Qualifiers.
The 32-year old has played 13 times for Tonga and three times for NSW City.
Mateo, who has a British passport, has made more than 200 career appearances in the NRL.