Alastair Cook's England form 'a big worry' - Ashley Giles

Alastair Cook has won 36 of the 69 games in which he has captained England

England captain Alastair Cook's form is a "big worry" ahead of the World Cup in Australia and New Zealand, says former one-day coach Ashley Giles.

Cook, 29, said he will have to "wait and see" if he will keep the captaincy after England were beaten 5-2 in a one-day series in Sri Lanka.

England's 15-man World Cup squad must be named by 7 January, with their first match against Australia on 14 February.

"Cook simply isn't playing that well," said Giles. "He is under pressure."

England selectors James Whitaker, Peter Moores, Angus Fraser and Mick Newell will announce a 16-man squad on Saturday for a tri-series next month in Australia against the host nation and India.

Head coach Moores said Cook's position will be reviewed this week. The Essex left-hander scored 119 runs in six matches in Sri Lanka, with a top score of 34.

"He hasn't been playing that well for a year and going into a World Cup your leader is important," Lancashire coach Giles told BBC Sport.

"But so is having 15 players in that squad who can perform and win games for England."

Cook has been England's one-day captain since 2011 and was appointed Test captain the following year.

Giles, England's limited-overs coach from November 2012 to April 2014, added: "I think there's still some discussion to be had and from the sort of the whispers we're hearing from the camp clearly they're not 100% sure.

"He is desperate to do well but he is still not getting the output that he would or England would want.

"In the last one-day match, he was dropped twice before he was finally out, so he is riding his luck - but he is not capitalising on it and it's becoming a problem."