The duo have forged a good understanding at international level for the England U21s and Irwin is confident that rapport will continue to grow at club level.
"Ferdinand and Vidic are obviously United's first choice but Phil and Chris are a great pair to have in reserve," the Treble winner told ManUtd.com.
"I've seen quite a bit of Phil and he certainly looks to be a top player. He's a big lad and you saw from watching him play for the U21s recently that's he more than capable of holding his own. And he's only going to get better playing at a club like this.
"Chris had an excellent first season last year. He probably played a lot more games than he thought he would but he never let anyone down even in the big games.
"Not only is he strong in the air, he's also got very good feet for a centre-half. Both he and Phil are big, strong lads with great talent."