Hartley was shown the red card playing for Northampton against Leicester in a Premiership match two weeks ago for elbowing an opponent.
"He will have been disappointed in himself to put himself in that position," Lancaster told reporters. "I will have a conversation with him."
Hartley was sent off in last year's Premiership final against Leicester and received an 11-week ban which ruled him out of the British & Irish Lions tour of Australia.
He was suspended for three weeks for his latest offence but will be available for the start of the Six Nations in February.
(Reporting by Ed Osmond; Editing by Mark Lamport-Stokes)
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