Wales outside-half Dan Biggar will make an early return against his former Ospreys side when he lines up for Northampton at Bridgend on Saturday.
Biggar, who starts on the bench, joined the Saints for the 2018-19 season after 11 years with the Ospreys.
Cardiff Blues and Dragons will also be in pre-season friendly action on Saturday.
Blues host Leicester while the Dragons travel to English Championship club Ealing Trailfinders.
Ospreys host the Saints at Bridgend’s Brewery Field with Tom Williams and Luke Morgan starting on the wings for Allen Clarke’s side after last month’s Sevens World Cup.
Both suffered facial injuries after an alleged tunnel altercation with Samoan Gordon Langkilde.
The Blues home game against the Tigers will be head coach John Mulvihill’s first in charge, with Wales wing Tom James set to make his return after being treated last season for depression.
Dragons will give debuts to several summer signings.
Bernard Jackman will try out the new-look half-back pairing of Rhodri Williams and Josh Lewis, with fit again Gavin Henson on the bench.
Ryan Bevington also gets his first start, with fellow Wales international Richard Hibbard among the replacements.
Scarlets begin their pre-season friendlies against Bristol Bears at Carmarthen Park on 18 August.
Cardiff Blues: Dan Fish; Jason Harries, Harri Millard, Willis Halaholo, Tom James; Steven Shingler, Lewis Jones; Brad Thyer, Ethan Lewis, Scott Andrews, Ben Murphy, James Down, Callum Bradbury, Olly Robinson (capt), James Botham.
Replacements: Liam Belcher, Rhys Carre, Keiron Assiratti, Rory Thornton, Alun Lawrence, Dane Blacker, Ben Jones, Cai Devine, Morgan Allen, Tom Williams, Aled Summerhill, Cameron Lewis, Ioan Davies.
Ospreys: Dylan Moss; Tom Williams, Joe Thomas, Cory Allen, Luke Morgan; Sam Davies, Tom Habberfield; Rhodri Jones, Scott Otten, Ma’afu Fia, Lloyd Ashley, Adam Beard, Guido Volpi, Sam Cross, Rob McCusker (capt).
Replacements: Ifan Phillips, Alex Jeffries, Tom Botha, Giorgi Nemsadze, Morgan Morris, Reuben Morgan-Williams, Luke Price, James Hook, Dewi Lake, Mitchell Walsh, Will Jones, Matthew Aubrey, Cai Evans, Kieran Williams, Hanno Dirksen, Dewi Cross, Chris John, James Ratti.
Dragons: Jordan Williams; Jared Rosser, Adam Warren, Jack Dixon (capt), Joe Goodchild; Josh Lewis, Rhodri Williams; Ryan Bevington, Rhys Lawrence, Lloyd Fairbrother, Joe Davies, Matthew Screech, Huw Taylor, Nic Cudd, James Benjamin.
Replacements: Richard Hibbard, Gerard Ellis, Brok Harris, Rynard Landman, Brandon Nansen, Lewis Evans, Rhodri Davies, Jacob Botica, Gavin Henson, Jarryd Sage, Tiaan Loots, George Gasson.