Mallinder unhappy at sinning Saints
Hartley, who led England to a Grand Slam and steered them to an unbeaten year of 13 wins in 2016, was a second half replacement in what turned out to be a 10-37 home defeat against Leinster.
He was given an instant red card by French referee Jerome Garces for a head-high, swinging arm tackle on Sean O'Brien.
Northampton have had two players banned in the past fortnight, with flank Calum Clark and prop Kieran Brookes both missing the Leinster match through suspension.
Now Hartley, who has already received 54 weeks of suspensions during his career, will miss the return game in Dublin next weekend.
"I don't need to talk about my reaction, it's what it's done to the team. Clearly players don't do it on purpose but you have to be very careful.
"We have spoken about it and we have had our disciplinary issues in recent weeks – it continues to haunt us. We are certainly not going out on the training field and practising high tackles.
"They do occur but it is happening too much for us and it is ridiculous what's gone on. When your international players come back, you want them to play and perform for you," Mallinder said.
Mallinder's men conceded the first of five tries in less than two minutes when a Rob Kearney break paved the way for Garry Ringrose to score his first Champions Cup try.
But the Saints battled their way back to 10-10 before conceding four second half tries, added to Hartley's red card and a yellow for replacement wing Ahsee Tuala undid them.
It means they now find themselves anchored to the bottom of Pool Four and are seven points adrift of leaders, Leinster. That makes the trip to the Aviva Stadium in Round Four a last chance for Mallinder and his team.
"We talked about getting off to a flying start but we didn't come out of the blocks as we wanted to. They are a quality side and they showed that.
"They put us under a lot of pressure and went points up but we came back well and scored a good try to get back in the game. But then we conceded and we really struggled when we went down to 14 men.
"But we have lost to Leinster at home before and gone on to win away. We just have to pull together – it is as simple as that. You can feel sorry for yourself and look at your injury and disciplinary problems, or you can let's get together and let's put it right," he added.
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