Celtics coach Doc Rivers said that captain Paul Pierce did not participate in any of Friday's practice session and remains "doubtful" for Sunday's season-opener against the Knicks on Christmas Day.

Rivers noted the team will attempt to put Pierce through a practice before departing for New York on Saturday and will consider playing him -- likely in a reserve role -- if he gains medical clearance.

Sasha Pavlovic is expected to start if Pierce, who has missed much of training camp and both preseason games with a bruised right heel, is unable to go.