Foster put his mistake against France when on England duty behind him with a string of superb saves as Lee Bowyer's goal secured a surprise victory over the leaders.
McLeish said: "I've always said a good keeper is paramount. He can win you championships, earn you points, save you points, or keep your team in the division.
"Ben has been superb for us. I thought the criticism of him with England was a bit harsh.
"He made some great saves here and in other games and has been on top form since he came here."