The Chesterfield boss says he’s well acquainted with Port Vale gaffer Michael Brown, who was a tough, uncompromising midfielder.
Brown accrued 105 yellow cards in a 476-game career and was sent off seven times.
Port Vale have been issued with a grand total of 86 cards in League One so far this season, 84 of them yellow.
Caldwell, a neighbour of the Valiants manager, said: “It will be a difficult game.
“I know the manager really well. He was a really aggressive player who had a fantastic career. I think his teams will play in a similar way.”
Caldwell and his assistant Steve Eyre embarked on a scouting mission in mid-week when Port Vale lost 3-0 Rochdale.
They sit two points above the drop zone today ahead of a visit to Chesterfield, who are second from bottom.
“They started pretty well actually and up until the sending off were in the game,” he said.
“Even after they showed a bit of fight and stuck at it.
“They’re fighting for their lives and I think every game in League One is competitive, tomorrow will be no different.”