Northampton director of rugby Jim Mallinder insists Dylan Hartley has let the club down after receiving a six-week ban after being sent off against Leinster.
Hartley will be available to lead England when they open the defence of their RBS 6 Nations crown against France on February 4, but he will not be back in Saints colours until late March.
The 30-year-old has made only five appearances for Northampton this season - three starts and two as a replacement - due to a back problem and this autumn's international commitments.
"The team is struggling a bit and we need some leadership from our senior players and we've lost that over the next few weeks"
Former England captain Lawrence Dallaglio accused him of "checking out" on his club, and Mallinder is dismayed by the swinging arm on Sean O'Brien that resulted in the third red card of his career.
"Dylan's letting the team down. He let the team down at the weekend. Any time you have a sending off and it's a disciplinary matter, you're letting the team down," Mallinder told BBC Radio Northampton, shortly before the six-week ban was announced.
"Dylan has had a lot of criticism. I can't say I'm not frustrated about it because clearly I am. The team lost a player at 50-odd minutes when we thought we were in the game.
"We've also lost him for the next few weeks when Mike Heywood really needs a rest. The team is struggling a bit and we need some leadership from our senior players and we've lost that over the next few weeks.
"We're frustrated about that, but Dylan Hartley is part of Northampton Saints. We've supported each over the last 10 years and will continue to do so."
Hartley had only been on the pitch for six minutes as a replacement when he struck O'Brien with a swinging right arm from behind, resulting in the Ireland flanker failing a head injury assessment.
The thee-man hearing that met in London upheld the decision of referee Jerome Garces to issue a red card, found that the offence was at the mid-range of World Rugby sanctions for the offence and chose a five-week suspension. Two weeks were added due to Hartley's poor disciplinary record before it was reduced by one week because of his guilty plea.
Before this latest red card, Hartley had amassed 54 weeks work of suspensions for offences including biting, gouging and butting and the total for his chequered career now stands at 60 weeks.