After the game, the team said Napoli suffered a dislocated finger and that X-rays were negative.
Napoli remained prone until trainer Rick Jameyson and manager John Farrell came out to attend to him. Replays showed his left ring finger bent at an unnatural angle.
Napoli had walked with one out and was advancing to second on a wild pitch uncorked by reliever Donnie Veal.
Last April, Red Sox second baseman Dustin Pedroia tore a ligament in his left thumb sliding headfirst into first base.
Two Red Sox regulars -- outfielder Shane Victorino and third baseman Will Middlebrooks -- are already on the disabled list, while Pedroia had missed Sunday's game with inflammation in his left wrist and did not start Tuesday. He entered the game as a pinch runner for Napoli.