The pundit believes the 'no nonsense' midfielder may not have seen eye to eye with the West Ham boss.
Indeed, while the 33-year-old was no longer at the requisite level to break into the Irons first team, Keown believes it was more an issue of the experienced midfielder taking a 'no nonsense' approach towards his manager.
When asked about Nolan's departure, the pundit replied during a 'Tackle Keown' session on the Daily Mail website:
"He felt like Sam’s brains on the pitch. I don’t think Allardyce did him any favours though, he earned that.
"He can still do a useful job for somebody, as long as his legs are still there. He is certainly a no nonsense person and I suspect he may not have seen eye to eye with Slaven Bilic. He may well have thought: ‘I don’t need this at this stage of my career’ so he’s off."
Keown's constant praise of Allardyce and suggestion Big Sam could even be turned to to save West Ham from a relegation battle have hardly endeared him to the Hammers faithful of late.
And fans certainly won't appreciate the suggestion it was solely the 33-year-old's decision to leave the club.
Then again, West Ham fans haven't taken too kindly to the idea of the east London side forcing Nolan out when they haven't yet signed a replacement in midfield - and may well end up going without one.
Could Nolan have lasted longer at Upton Park if Bilic was more understanding of his role? Or are the east London side going to be better off simply getting rid of a player that was no longer up to the right standards?