The round, however, kicks-off on Friday with three games, all featuring Welsh regions.
Cardiff Blues are at home to Connacht, who have not won at the Arms Park since 2001.
Newport Gwent Dragons entertain Edinburgh, with both teams looking for their second win of the season, while the Scarlets go north to Glasgow, where a win would take them top for at least 24 hours.
MAGNERS LEAGUE - ROUND 4 FIXTURES:
Friday, September 26 -
Cardiff Blues v Connacht, Arms Park, 7.05pm (live BBC Wales/Setanta Sports Ireland)
Glasgow Warriors v Scarlets, Firhill Arena, 7.30pm
Newport Gwent Dragons v Edinburgh, Rodney Parade, 7.30pm
Saturday, September 27 -
Ospreys v Ulster, Liberty Stadium, 5.30pm (live Setanta Sports 2/S4C)
Sunday, September 28 -
Leinster v Munster, RDS, 7pm (live Setanta Sports 1)