Kevin Pietersen believes England captain Alastair Cook remains in the role only to prevent "yet another PR disaster" for the England and Wales Cricket Board.
Pietersen, who was dropped by England in February following the Ashes whitewash in Australia, has urged under-fire Cook to seek help for his batting and relinquish his captaincy.
Cook has been under increasing pressure following a miserable run which has seen England lose seven of their last nine Tests and the 29-year-old score just 129 runs in nine attempts.
But the captain has time and again vowed to tough it out, and he remains in charge going into Sunday's third Test against India at the Ageas Bowl.
Writing in his column in the Daily Telegraph, Pietersen said: "At the moment only politics are keeping Cook in a job because the England and Wales Cricket Board backed him so much that it would be yet another PR disaster if it sacked him now.
"But the ECB needs his runs back more than anything else so a big decision has to be made. Forget the bad headlines for once.
"[Cook] should do what is right for England and resign the captaincy. He has shown he does not have the tactical brain to lead the side."
Cook has scored more Test hundreds than any other Englishman, and Pietersen said: "England badly miss Cook the opening batsman scoring 150 to set games up at the top of the order and, relieved of the captaincy, I don't think it is too late for him to rediscover this form."
Pietersen clashed with current England coach Peter Moores during the latter's first spell in charge, and he said: "Cook needs people with experience of international cricket around him, which Peter Moores and (assistant) Paul Farbrace lack.
"There are so many great cricket brains in the Sky studios. Put that radio in your ear, listen to them on the balcony or in the dressing room and Mike Atherton, Nasser Hussain, Shane Warne or whoever could be saying something you didn't know and could implement in the game."
Watch the third Test between England and India live on Sky Sports. Coverage begins at 10am on Sunday on Sky Sports 2