A 26-year-old man was brutally beaten in the Faneuil Hall area early Saturday morning, leaving him in critical condition, police said. Officers responded around 6 a.m. to Tufts Medical Center, where the victim was being treated for “life-threatening injuries,’’ according to a police report. Police learned that the victim had been attacked on 5 Clinton St., near several popular bars and restaurants. The victim’s name was not released, and police had no details on possible suspects or a motive. The Boston police homicide unit is investigating. The victim remained in the hospital yesterday in critical but stable condition, said Elaine Driscoll, a police spokeswoman.