The England hooker Dylan Hartley will not play again until after Christmas after admitting striking his opposite number Rory Best during Northampton's Heineken Cup defeat to Ulster at Franklin's Gardens last week. Hartley, who had only just returned to lead the Saints after missing four matches because of a knee injury, was cited for hitting Best with a forearm and received a two-week suspension at a disciplinary hearing in Dublin on Thursday.

The ban was increased by a week because of the hooker's poor disciplinary record – he received a two-month ban for biting the finger of another Ulsterman, Stephen Ferris, during England's Six Nations victory at Twickenham last March – but restored to two because of his guilty plea and the contrition he showed during the hearing which was heard by an independent judicial officer from Wales, Roger Morris.

Morris decided that Hartley, who was represented at the hearing by Richard Smith QC, did not commit a premeditated act and ruled that the offence came it at the low end of the disciplinary scale. Had it been at the top end, the forward faced missing the start of the Six Nations.

Hartley will miss the return match with Ulster at Ravenhill on Saturday and he will also be absent when Northampton take on the Premiership champions Harlequins at Franklin's Gardens the following week. He will return for the league clash with Saracens at stadium.mk at the end of the month.

"Dylan is our captain and talisman," said the Northampton director of rugby, Jim Mallinder. "It is a frustration to lose him. He came up against an old adversary in Rory Best, and although it was not a massive incident, it was something. All players have to learn about playing on the edge but not going over it.

"We will take the punishment and we will not be going to Ravenhill with our heads down. It is a massive game of rugby and we have spoken to the players about the opportunity they've got. We have to be up for the challenge."

Cardiff Blues will be without their Wales scrum-half Lloyd Williams for five weeks. He was sent off for a dangerous tackle on his opposite number Benoît Paillaugue during last Sunday's Heineken Cup defeat to Montpellier at the Arms Park and will be free to play again on 14 January, a week before Wales's Six Nations squad is due to be announced.