The BBC pundit isn't impressed with the Sunderland centre-back.
Indeed, Keown feels the centre-back should have done better during Southampton's equaliser at St Mary's on Saturday afternoon.
Sunderland drew 1-1 and O'Shea wasn't deemed to have utilised his experience enough when the Saints scored.
"Defoe is so sharp off the bench, I know because I played against him myself.
"It’s a great finish from [Virgil] Van Dijk but, with his experience, O’Shea has got to do better there."
This time last week, meanwhile, Keown compared O'Shea to a manikin after the Sunderland defender's performance against West Ham United.
On both occasions, fine margins cost the Black Cats - but not necessarily major mistakes. A week ago, Sunderland were beaten by one West Ham goal, while Southampton's late equaliser was one error throughout 90 minutes.
But those errors all pile up and, instead of four points from two games, Sunderland now have just one.
So is O'Shea a liability right now - or is Keown wrong to single out the 34-year-old?