Clarke will name his 26-man pool for this summer's finals on Wednesday afternoon ahead of pre-tournament friendlies against Holland and Luxembourg.
Here PA takes a look at the contenders for a place in the squad.
David Marshall and Craig Gordon are certainties and will battle it out for the jersey. Jon McLoughlin has been a regular in the past nine squads but only has two caps to his name. He has also spent much of the season at Rangers playing understudy to Allan McGregor, who has been urged to rethink his international retirement by the likes of Ally McCoist and Kenny Dalglish on the back of the incredible displays which saw him named the SPFL player of the year. St Johnstone's Zander Clark and Liam Kelly, fresh from a loan spell at Motherwell from QPR, have been pushing their case in recent months too.
Skipper Andrew Robertson will be the first name down on the team sheet ahead of the Scots' opening clash with the Czech Republic. Kieran Tierney has shaken off a knee injury that at one stage was feared would rule the Arsenal star out of the tournament. The likes of Declan Gallagher, Scott McKenna, Grant Hanley, Stephen O'Donnell and Jack Hendry seem destined to go but Greg Taylor, Andy Considine and Liam Palmer will be sweating on their involvement. Leeds captain Liam Cooper was left out of March's World Cup qualifiers while the Hibs trio of Paul Hanlon, Paul McGinn and Ryan Porteous have also been involved recently too and are looking to end the season on a high by lifting the Scottish Cup. Nathan Patterson makes up for what he lacks in experience with huge potential and the Rangers youngster could be a wildcard pick.
Clarke has already suffered a couple of significant blows to his plans after Ryan Jack and Kenny McLean were both ruled out through injury. But the Scotland boss is well stocked in the centre of the park. Scott McTominay, John McGinn, Callum McGregor, Stuart Armstrong, Ryan Christie and John Fleck will all be expecting an invite but the absence of Rangers midfield anchor man Jack means there is a dearth of players whose expertise is more on the defensive side of the game. That might open the door for Jack's former Ibrox team-mate Ross McCrorie to step up from the under-21s. But if Clarke is looking to be bold then he may decide it is time to roll the dice on the likes of Billy Gilmour, Ryan Gauld and David Turnbull.
Che Adams and Lyndon Dykes have established themselves as the main men up top but Clarke has dabbled recently with his front-line combinations. Ryan Fraser's pace makes him a useful alternative while James Forrest is set for a recall after an injury-interrupted campaign with Celtic. Oli McBurnie ruled himself out on Monday after a fractured foot brought a premature end to a miserable season for the relegated Sheffield United striker. Hibs striker Kevin Nisbet looks to have nudged ahead of Lawrence Shankland, Oliver Burke and Callum Patterson in Clarke's pecking order but with 26 names to pick, might the Scotland boss decide Leigh Griffiths' poaching skills are worth a call-up despite his frustrating season with Celtic?