Root no certainty to suceed Cook: Strauss

England's director of cricket Andrew Strauss insists Joe Root replacing "drained" Alastair Cook as Test captain is not a done deal, but admits the 26-year-old is a leading candidate for the role.

Cook announced his resignation on Monday following four and a half years as skipper, and Root is now the outstanding favourite to take charge.

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Root's leadership experience is limited, but he has served as vice-captain under Cook as well as becoming England's most reliable batsman since making his Test debut against India in 2012.

Enigmatic allrounder Ben Stokes is another potential contender, along with experienced pacemen Stuart Broad or James Anderson, but it would be a huge surprise if any of them were preferred to Root.

Strauss however says the Yorkshireman is not an automatic pick.

"Is it a given? I don't think so," Strauss said. "It's right we follow a process with this.

"There are a number of players playing informal and formal leadership positions, and it's right that we have conversations with all those guys."

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One of Strauss' first moves upon taking up his role as England's director of cricket was however to appoint Root as Cook's understudy, and he has been impressed with his approach.

"It's worth saying I think he's done a very good job as vice-captain," Strauss said.

"He's obviously matured a lot over the last couple of years or so and there's absolutely no reason why he won't be one of the strong candidates for the role."

After 53 Test matches, Root averages 52.80, having scored 11 centuries and 27 half-centuries.

One concern is the captaincy could hamper Root's brilliant form, while another is that he will have less than a year in the job before undertaking the most formidable task in English cricket - leading an Ashes series in Australia.

But Strauss, who preceded Cook as Test captain, suggested neither of those potential issues would seriously harm Root's chances.

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"Any England captain, no matter how good they are with the bat or otherwise, there are challenges to the role," the 39-year-old said.

"If you're one of the better players, it gives you more chance not to have to worry about your own performance.

"One of the unique challenges of being England captain is you have to perform at the same time as doing all the other jobs that this role entails."

The expectation is that Root would offer a more aggressive style of captaincy than Cook, who led from the front with his relentless run-scoring but was a self-confessed conservative leader and tactician.

Cook releases the captaincy after a national-record 59 Tests in charge, which included Ashes series victories in 2013 and 2015, as well as notable successes in both South Africa and India.