'The Cobra' meets Groves in a rematch of their clash from last November at Wembley on May 31, and Calzaghe, who retired with an unbeaten record, thinks that Froch has the edge of his opponent.
The Telegraph quotes the Welshman as saying: "Everybody is different. You can train as hard as you want, certain fighters can keep going, others can't. Some people haven't got 12 rounds in them at a fast pace.
"One thing about Froch [is], he keeps coming. You need to nail the guy down. So he will always be dangerous.
"It's whether Groves can keep that style for 12 rounds, because he is going to need to. Groves will have to improve and will have to have learnt from that first fight."
Froch was victorious in their first bout last year, after a controversial stoppage.