Nortel Networks Chief Operating Officer Clarence Chandran will take a medical leave of absence in order to fully recuperate from two recent surgeries related to injuries stemming from a 1997 stabbing in Singapore, the communications equipment company announced Tuesday. Chandran, on the advice of his doctor, will take between six and 12 months off work. Chief Executive John Roth will handle Chandran's duties during his absence. A current nominee for the Nortel board of directors, Chandran is expected to serve if elected. A vote is expected in late April.