Essex’s Cox, an aggressive 23-year-old right-handed batter, was part of England’s Test squad for the series against Sri Lanka which concluded on Monday but did not play.
He was also the top scorer for men’s champions Oval Invincibles in this year’s Hundred, scoring 214 runs in seven matches with a strike-rate of 143.62.
Barbados-born Bethell first emerged as part of England’s Under-19 squad that were runners-up at the 2022 World Cup.
The left-hander, who also bowls left-arm spin, scored 166 runs in seven innings for Birmingham Phoenix in the Hundred this year and was part of the Birmingham Bears side that reached the quarter-finals of the T20 Blast.
He moved to England as a 13-year-old after receiving a cricket scholarship at Rugby School.
Bethell’s Warwickshire team-mate Dan Mousley, Hampshire seamer John Turner and left-armer Josh Hull, who made his Test debut in the third Test against Sri Lanka, are the other uncapped players in England’s squad but have been overlooked for Wednesday’s series-opener.
England omitted Jonny Bairstow and Moeen Ali – the latter has since retired from England duty – from the squad but seven of the T20 World Cup squad from earlier this year make the XI.
Salt, who will also keep wicket in Buttler’s absence, will open with Will Jacks, while all-rounders Liam Livingstone and Sam Curran, plus bowlers Adil Rashid, Jofra Archer and Reece Topley keep their places.
Surrey’s Overton will play as a batter only as he recovers from a back injury.