Dylan Hartley lasted just six minutes off the bench after he was red-carded in Northampton Saints' 37-10 defeat to Leinster in the European Rugby Champions Cup at Franklin's Gardens.
The England captain, who is no stranger to controversy in his career, was sent off after 58 minutes for a swinging arm to the back of the head of Leinster flanker Sean O'Brien.
The incident could have blown his chance of captaining the British and Irish Lions on their tour of New Zealand next summer.
The 30-year-old has served 54 weeks of bans during his career for offences which include eye-gouging, biting, head-butting and swearing at a referee.
He looked to have turned over a new leaf since being given the England armband by Eddie Jones.
But his latest indiscretion not only left his club in the lurch, but overturned that reputation as a reformed character.
Head coach Jim Mallinder offered no consolation.
Saints finished the match with 13 men after replacement forward George Pisi was yellow-carded for a high tackle.
It tops a difficult week for the Saints after their handling of a head injury suffered by George North at Leicester last week came under severe scrutiny.