Former Sheffield United manager thinks highly of the Sheffield Wednesday boss.
Warnock spent eight years in charge of their rivals Sheffield United, and took plenty of stick upon his recent visit to Hillsborough, but left the ground smiling.
Warnock led Rotherham to a surprise win against Wednesday last month, but said he was impressed by the Owls' Portuguese manager.
Wednesday are in the promotion hunt despite that surprise defeat, and are currently on course to make the play-offs, sitting in sixth position in the Championship.
Warnock said: "Not many people will want to play them over two legs. They are solid at the back and score goals. It's as good a Wednesday team as I've seen."
Discussing Carvalhal, he added: "I think he's a good manager.
"He enjoys the banter with the players, and he's got confidence in the players. He's got certain principles, gets a system to suit the players, and changes a little bit when he has to."
He admitted he had not heard of Carvalhal prior to his appointment at Hillsborough, but can tell he is a manager with a good grasp of the game.
The results have shown that so far too, with the Owls doing exactly what supporters had hoped for.
They got back on track ahead of the international break, winning their last two games after a run of five matches without a victory.