Compton, grandson of England great Denis, has opened for England alongside captain Cook in their last nine Tests but could only manage 39 runs in four innings in a 2-0 home series win over New Zealand last month. Root, thus far for England a middle-order batsman but an opener with Yorkshire, has been in fine form this season and scored his maiden Test hundred, against New Zealand, on his Headingley home ground.
Compton, however, will have an excellent chance to restate his case when south-west side Somerset, his county, play Australia in a four-day warm-up match in Taunton starting Wednesday.
But he will not play for England against Essex, Cook’s county, at Chelmsford, east of London, this coming weekend.
“We believe Joe Root is currently the best opening partner for Alastair Cook, and he will open the batting against Essex,” said England national selector Geoff Miller in a statement.
“Joe has performed well for Yorkshire at the top of the order earlier this season, and during his international career so far has proven to be very adaptable in all three formats and relished the challenge of international cricket,” the former England off-spinner added.
England named a 14-man squad for the match, beginning on Sunday, and are expected to finalise a 12 or 13 a week or so later for the first Ashes Test at Trent Bridge starting on July 10.
Former Ireland international Boyd Rankin is the only member of the squad to face Essex who has yet to play for England in any format.
Rankin, Onions and a fit-again Kevin Pietersen are the only players selected who were not named in either a Test or one-day squad to face New Zealand at the start of this season.
Miller added: “This match is a vital part of our preparations for the Ashes after a period of limited-overs cricket for a large number of the squad. We have a very exciting two months of Test cricket coming up, and it is important we start well at Chelmsford next week.
“Kevin Pietersen has had no complications following his recent return to cricket after a knee injury — which is pleasing — and Graeme Swann is recovering well from a calf injury.”
Swann, England’s leading off-spinner, played in just one of the hosts’ matches in the Champions Trophy and missed Sunday’s final loss to India at Edgbaston on Sunday
Star batsman Pietersen, out of action since March because of right knee bruising, returned in style by making 177 not out for Surrey against Yorkshire in the County Championship on Sunday in his first innings of the season.
Ashes-holders England will be bidding for a third straight Test series win over Australia — something they last achieved in the 1950s.
Alastair Cook (c), James Anderson, Jonny Bairstow, Ian Bell, Tim Bresnan, Stuart Broad , Steven Finn , Graham Onions, Kevin Pietersen, Matt Prior (wk), Boyd Rankin, Joe Root, Graeme Swann , Jonathan Trott