The midfielder told manutd.com: "Overall, Rio sticks in my mind. He has been immense all season. There are games that stand out - Liverpool at Anfield in the league, and the away matches in Europe against Barcelona and Roma. He has been awesome.
"Not much gets past him and it's a great comfort for a midfielder like myself to have a player that good backing you up. His performances are consistently at a high standard. The thing is, he's getting better. Being made England captain and taking the armband in some United games has given him a boost. This season he's probably proved he's the best defender in the world."
Asked who he voted for in the PFA's Player of the Year, Carrick added: "I picked Ronny because he scored a hatful of goals and so many were important. A winger getting 42 goals is hard to ignore. He'll get praise from all angles, and rightly so, but Rio has been unbelievable and defenders often get overlooked. The back line as a whole has been magnificent and Rio has been a big part of that. In any other year Rio would have been Player of the Year."