The procedure took place Tuesday, Mariners interim manager Daren Brown said.
It will take Bradley between four to six weeks to rehabilitate the knee, which means he may not return in 2010.
Asked if Bradley could be sidelined for the rest of the season, Brown said, "That's what it looks like."
Brown did, however, said Bradley could return if he can bounce back in four weeks.
Bradley was placed on the 15-day disabled list on July 31, retroactively to July 27. The switch-hitter was batting .205 with eight homers and 29 RBI in 73 games.
His batting average from the left side of the plate was .191.