Nick Williams has signed a two-year extension to his contract at Ulster which keeps him at Ravenhill until 2016.
Ryan Jones has suffered a new injury setback and is ruled out of making his comeback against Ulster on Friday.
Edinburgh have suffered a blow with the news that Perry Parker has been ruled out for up to four months.
The Ospreys joined Glasgow at the top of the RaboDirect PRO12 table after a 43-26 victory over Connacht in Galway.
Richard Cockerill believes players will remain loyal to their clubs over England as the dispute over Europe rumbles on.
Paul O'Connell made a successful return in Munster's workmanlike RaboDirect PRO12 win over the Newport Gwent Dragons.
Returning Lions Tommy Bowe and Rory Best made the perfect return to Ulster colours as the hosts beat Treviso 32-13.
Leinster forwards coach Jono Gibbes will join Clermont Auvergne at the end of the season.
Leinster claimed a bonus point 34-20 win against Cardiff Blues at the RDS.
Scarlets battled their way to a 22-9 victory at Edinburgh, scoring tries through Nick Reynolds and Jordan Williams.
Glasgow maintained their perfect start to the RaboDirect Pro12 season with a 24-17 victory over Zebre.
The Welsh, Irish and Scottish Rugby Unions will not sanction their clubs getting involved in a breakaway
Ospreys welcome back Justin Tipuric for their clash with Connacht, while Paul O'Connell is named on Munster's bench.
Sam Warburton will make his first appearance of the season for Cardiff against Leinster after recovering from injury.
British & Irish Lions captain Sam Warburton is set to make his comeback from injury for Cardiff Blues on Friday night.
Edinburgh have added to their pack with the signing of No 8 and Hawke Bay skipper Mike Coman on a two-year contract.