Caldwell's Scotland takes on Ramsey and Wales tonight.
The Wigan defender said: “I don’t know what happened that day but Ramsey was outstanding. He ran the whole game and caused us so many problems.
“He’s definitely one of two or three world‑class players in their team.
“If we don’t deal with them they are going to cause problems this time too. But I certainly believe we can go there and win.”