London: Alastair Cook was "drained" by the demands of being England test captain and felt new blood was needed in the role, England director of cricket Andrew Strauss said on Monday.
Cook, 32, quit as skipper after four-and-a-half years and a record 59 matches in charge.
"He was getting drained by the relentlessness of being England captain," Strauss told the BBC.
England lost a test series 4-0 in India at the end of last year, prompting Cook to stand down.
"In my conversations with him in January it became clear that Alastair felt a huge amount of energy, drive and determination was needed to drive the team forward over the next 12 months."
Cook, England's leading run-scorer in test cricket, led the side to two Ashes victories but the team under-performed in 2016 during which they lost eight test matches.
"He feels it is time for new blood, new impetus and fresh thinking and allowing someone else to take over and do that."
Joe Root is strong favourite to replace Cook at the helm but Strauss said he was not ruling anyone out of the running ahead of home series against South Africa and West Indies this year before the next Ashes contest in Australia.