Defending champions the Ospreys currently lie in fourth place and they have a crucial visit to Scotstoun Stadium to play third-ranked Glasgow on Friday night.
Having lost to another play-off contender, the Scarlets, last time out, the Warriors have slipped to their lowest point in the table since Christmas. If they are to have any hope of retaining their title, the Ospreys know how important a victory would be this weekend.
Leaders Ulster are also in action on Friday night, facing a derby trip to ninth-placed Connacht. Mark Anscombe's men must be wary of the fact that Connacht have not lost at the Sportsground in 2013 and won this equivalent fixture last season.
The fifth-placed Scarlets will have a chance to catch up on the top four when they face the Cardiff Blues on Saturday, knowing they have won their last seven matches against the Blues in all tournaments.
The final match of the round sees second-placed Leinster breaking new ground when they take on Zebre at the Stadio Citta del Tricolore in Reggio Emilia, Italy.
It is the first time a RaboDirect PRO12 fixture has been played there, the game has been moved to the larger venue to help raise funds for victims of the earthquake that hit the region last year.
RABODIRECT PRO12 - ROUND 21 FIXTURES:
Newport Gwent Dragons (11th) v MUNSTER (6th), Rodney Parade, 7pm
Glasgow Warriors (3rd) v Ospreys (4th), Scotstoun Stadium, 7.35pm (live BBC ALBA/BBC 2 Wales)
CONNACHT (9th) v ULSTER (1st), the Sportsground, 7.45pm (live TG4/BBC 2 Northern Ireland)
Benetton Treviso (7th) v Edinburgh (10th), Stadio di Monigo, 8.30pm local time (live SportItalia 2)
Saturday, April 20 -
Scarlets (5th) v Cardiff Blues (8th), Parc y Scarlets, 6.30pm (live S4C)
Sunday, April 21 -
Zebre (12th) v LEINSTER (2nd), Stadio del Tricolore, Reggio Emilia, 4pm local time/3pm Irish time (live RTÉ Two/SportItalia 2)