Ferguson stepped down as manager of United this summer after a successful 27-year in charge, moving upstairs to become a director at the club.
The Red Devils have struggled under new boss David Moyes, losing five and winning just six of their opening 15 matches to sit ninth in the Premier League table, and Keane believes that Ferguson's desire to control everything at the club is one of the reasons behind their poor form.
"Everything is about control and power. He's still striving for it now even though he's not manager. There's massive ego involved in that," Keane told an ITV4 documentary detailing his rivalry with former Arsenal skipper Patrick Vieira.
Keane and Ferguson have had a number of public disputes since the former left United in 2005 after a fallout with the Scot.