Clarke has his own selection issues. The news of Aaron Hickey is not good, so who plays right-back against the speed and blood-curdling trickery of Vini Jr?
Nathan Patterson, Anthony Ralston, or does Clarke go rogue and ask Kieran Tierney to do one of the least enviable jobs in football? There's sense in that. Tierney has vast experience. This is a day for nous.
Who does Clarke play up front - and is there any prospect that whoever it is might have more than crumbs to feed on?
Che Adams runs hard, but he's unconvincing. Lyndon Dykes is a battering ram, but Gabriel and Marquinhos have seen his sort before in their storied careers. Lawrence Shankland, Ross Stewart and George Hirst are the other contenders.
There is logic in putting Scott McTominay into the role - a curveball for Brazil - but Steven Naismith, assistant manager, dismissed it the other day.
McTominay is big and strong, incredibly energetic, a proper handful and a superb finisher. He has not been at his best in the two games, not even close to his best, but there's always the threat of him sparking to life.
It's got to happen now. It's got to happen for John McGinn, too. It's got to happen for Ben Gannon-Doak, the potential difference-maker out wide.
He was utilised off the bench against Morocco, Clarke hoping he'd have a bigger impact when the game was looser and the space was opening up. Gannon-Doak will start on Wednesday.
Scotland's strength is their endeavour, their hard work, their passion, but those things only get you so far. There is some technical ability in there, but not masses of it.
What was said before Haiti and Morocco is still relevant now - Scotland's big-name players need to step it up. They need to be better, they need to create and be ruthless.
So many things need to happen for Scotland to get a point, or three, from this game, but if they do then the joyous fortnight-long scenes in Boston, a city that adopted the Tartan Army as their own, will feel like a warm-up act.
It's a racing certainty that the Scotland fans, in their revelling and in their bevvying, have extra gears in them. The great hope is that Clarke and his players, in their pursuit of history, have a whole lot more to show in what could be the game of their lives.