Ex-England captain Michael Vaughan believes the West Indies have exposed a "fragility of a technique" in current No.3 Tom Westley.
Westley debuted against South Africa last month and has passed 30 once in six innings, having failed twice so far against the Windies with eight in the first Test at Edgbaston and three in the first innings of the ongoing Test in Leeds.
Quick Single: Brathwaite, Hope centuries defy England
"In two innings against West Indies he has played across the line twice," Vaughan was quoted as saying on BBC.
"It is a real issue for him. Batting at number three you can't have that fragility of a technique.
"(If you) bowl a (good) channel his head falls over to the off side and he finds it difficult to get a stride in.
Quick Single: Live - Bangladesh v Australia
"That front foot has to be flat on the ground when you are playing a drive or forward defensive. For his wicket he is on his tip toes with his front foot. He has no balance at all.
"Only a few Test matches into his career so far, I think he has been worked out."
Right-hander Westley was selected off the back of strong form for Essex in the County Championship, where he has made two hundreds and two fifties in eight matches this season at an average of 53.11.
The 28-year-old made a patient second-innings 59 against a strong Proteas pace attack on debut at The Oval, however the manner of his two lbw dismissals concerned Vaughan, who sees problems with not only Westley but also fellow Ashes hopefuls Mark Stoneman, who has made eight and 19 in his first two Tests, and Dawid Malan, who made 65 in Manchester but missed out with eight in the first innings at Edgbaston.
"These players have got an opportunity to get on the trip to Australia and all three have made mental or technical mistakes," Vaughan said.
"The selectors will be concerned. They will be supportive to the public and in the media but privately will have real concern."
The issue has been an ongoing one for England, who are now racing against the clock to solidify their top six ahead of the Ashes trip to Australia in November, with only Alastair Cook, captain Joe Root and allrounder Ben Stokes guaranteed of top six places.
Quick Single: Brathwaite rebounds from horror week
On the eve of the second Test, Root called out the rookie trio, suggesting that now was the time to seize the chance they have been given.
"I think the only message for those guys is to go out there and take this opportunity," he said. "If they want to nail down those spots they have to deal with the pressure and, if they get in, make it really count."
With West Indies boasting a strong lead after the heroics of Shai Hope (147no) and Kraigg Brathwaite (134) on day two, all three batsmen are set to spend more time in the middle before the match is out, with the third and final Test beginning on September 7 at Lord's.