The 52-year-old actor was in Camden, north London, when the incident happened on Saturday, and is thought to have occurred after a scuffle with another man about glamour model April Summers.
The 'Silent Hill' star was at the Hill Bar and Brasserie smoking outside when a passer-by began making comments about April – real name Nadia Foster – and Sean followed the man down the road to challenge him.
Later when Sean went out for another cigarette, the man returned and stabbed him in the arm with what is believed to be a broken glass, and also punched him in the face.
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However, he refused hospital treatment and returned to the bar afterwards.
A source at the bar told the Daily Mail newspaper: "Sean is a regular here and we've never had any problems before. He was with a very attractive woman and an incident occurred outside the bar.
"He came in with a cut on his arm and bruise on his eyebrow. We saw to his injuries with a first aid kit. He seemed OK and wanted to have another drink."
It is not known if April – who is 30 years younger than Sean – is his new girlfriend, following his split from his fourth wife Georgina Sutcliffe in December 2010 after two years of marriage.