But he returned in time for Munster's Heineken Cup quarter-final and produced a totemic display to see off the champions of England Harlequins.
Such has been his revival that Warren Gatland felt obliged to pick him for the Lions tour to Australia where he has been tipped by many to renew his second-row pairing with Alun Wyn Jones of four years ago.
But Jones, who led Australia to the World Cup final in 2003, remains unconvinced as to whether O'Connell can last the pace in Australia.
"Lock is a position where I feel the Lions are a little lacking," Jones told the Irish Examiner.
"The great Paul O'Connell is fading. He may have one great Test in him, but three on successive weekends will be difficult."
In the back-row competition is so strong that England captain Chris Robshaw did not even make the plane but for Jones it is O'Connell's compatriot Sean O'Brien who could be the decisive figure in the series.
"The Welsh pair of captain Sam Warburton and Toby Faletau are standouts in the Lions back row," Jones said.
"Warburton is hard on the ball and Faletau possesses a nice step not dissimilar to the great Toutai Kefu, who helped Australia to win the World Cup in 1999.
"Sean O'Brien, the Irish flanker, was massive against the Wallabies in the upset at the 2011 World Cup so I see this trio ensuring the breakdown contest is relentless."