The England striker had a second knee operation and will start an intensive rehabilitation programme immediately.
Manager Graeme Souness' dismissal comes following the club's poor run of form this season.
Michael Owen could play for the first time since the 2006 World Cup in the Premier League game at Reading.
Alan Shearer broke Newcastle United's goal-scoring record in a 2-0 home win over fellow strugglers Portsmouth.
West Ham United sacked manager Alan Pardew on Monday after a poor run of results left the club third from bottom in the Premier League.
Nigeria striker Obafemi Martins left Inter Milan for Newcastle United for a fee of 15 million euros.
James Beattie struck two minutes into injury time to give Southampton a 1-0 Premiership win at West Ham United on Monday.\n\n