The two-time World Cup forward has played 36 Tests for Fiji and has plied his trade in the first and second divisions in France since 2016, most recently for Top 14 outfit Clermont.
Scrum weapon and tackle buster Tupou has been a focal point of coach Brad Thorn’s plan at Ballymore.
But the Wallabies prop is unlikely to feature this season after tearing his achilles tendon on last year’s European tour.
He is facing a race against time to be fit for September’s World Cup.
Ravai, who can play on both sides of the scrum, began in the now-defunct National Rugby Championship for the Greater Sydney Rams in 2014 before a stint in New Zealand.
The Reds play the Western Force in Perth on Saturday, one of just two warm-up clashes before their season begins against the Hurricanes in Townsville on February 25.