Cahill twice hauled his side level and Ashley Young missed a penalty before substitute Ivan Klasnic struck four minutes from time to claim the points for the home side.
Coyle said: "With his age, Gary is only going to get better. I believe he could play for any top team in world football. Gary could stand toe to toe with anyone."
Coyle is resigned to losing Cahill at some stage - possibly this summer - but claims he will not stand in the way of his departure at the right price.
"There will be a time when Gary has outgrown this football club and when that time comes it wil take good money but he will go with my blessing," added Coyle.
"I will never stand in the way of anyone progressing. What Gary has to do between now and the end of the season is keep showing these top clubs what an unbelievable talent he is."