Fetu'u starred in Tonga's warm-up games, scoring a try against Fiji, and played a huge role in their narrow loss to Canada in the World Cup pool stages.
The 26-year-old winger who was born in Tofoa, scored Tonga's winning try in their pool victory over Japan.
The province's head coach Eric Elwood will announce his starting line-up and replacements on Friday afternoon.
CONNACHT Squad - Backs (11): Paul O'Donohoe, Frank Murphy, Matthew Jarvis, Miah Nikora, Niall O'Connor, Tiernan O'Halloran, Brian Tuohy, Henry Fa'afili, Eoin Griffin, Fetu'u Vainikolo, Gavin Duffy.
Forwards (14): Rodney Ah You, Ronan Loughney, Dylan Rogers, Brett Wilkinson, Adrian Flavin, Ethienne Reynecke, Michael Swift, David Gannon, Mike McCarthy, George Naoupu, John Muldoon, Johnny O'Connor, Ray Ofisa, Thomas Anderson.