Scotland, with Hearts’ Lawrence Shankland replacing Dykes up front, missed a series of chances in Portugal and Clarke also thought “it comes down a little bit to confidence”.
“Shanks didn’t really have any clear-cut chances where you are thinking ‘go on, he’s getting there’,” he said.
“It’s maybe something we need to look at – his positioning, especially on set-plays, where he was maybe too far out from the centre of goal. There are always things you can look at.
“What can we do about it? Keep practising in training.”
Clarke was talking before it was announced that Liverpool winger Ben Doak had joined Dykes in leaving the provisional squad, with Bristol City striker Tommy Conway called up from the under-21s as a replacement.
“Don’t forget these players are nervous,” Clarke added. “They have the biggest tournament coming up for the country next week. They all have half a mind on Germany already.
“It sounds terrible to say that, but that’s just the way it is. It’s natural.
“They want to go on the plane flying to Germany for the Euros and they are involved in what’s going to be a fantastic tournament in the summer, so you have to make allowances for that.
“People won’t think of that. They just think of the excitement, etc. But, until you are actually on the plane and on the way to Germany, there is always a doubt in the back of your mind.”
