Although, as expected, the squad has a familiar feel to it, Clarke was clear there is still room for players to play their way into the group who will head to the United States in June, when they will take on Haiti, Morocco and Brazil.
He said there were four more players who he wanted to have in the squad for the games against Japan and Ivory Coast, but injuries deprived him of that chance.
“There are some players I feel I need to have a look at,” Clarke explained. “A lot can change over the next 10 weeks before you pick your final squad.
“Hopefully, no significant injuries but it can happen and has happened to us before, so we have to be ready to cover all the bases.
“There are a few players who could have been in the squad and are not in the squad – but I know what they can do.
“I’ve got other players in the squad where I’m maybe not convinced yet about what they can and can’t do. So, let’s have a look and see what happens.
“There is always room for someone else, an outsider.”
Only Curtis, Sparta Prague midfielder Andy Irving and Wrexham centre-back Dom Hyam are fresh faces from November, once regulars returning from injury are discounted.
Hyam, who is playing every week for a Wrexham side in play-off contention in the Championship, may have the most to gain if given time to show what he can do.
Nathan Patterson, who has had a tough time dealing with injuries at Everton, also has a major chance to prove he is the man to deputise for Aaron Hickey at right-back after starting his Scotland career strongly before his move to England.