Giggs turned 40 on Friday and has played for the Red Devils for 23 years, and the former Wales captain heaped praise on the United man.
"He's achieved everything in the game, a true once-in-a-lifetime player and the fact that he is still playing and excelling at the highest level speaks volumes about the man," Horne wrote in his Liverpool Echo column.
"I had the honour of captaining Ryan for Wales and the nightmare of playing against him as I came towards the end of my career.
"I was the man who dummied the ball before Ryan smacked it into the top corner of the net [for his first Wales goal]. I wonder if he still owes me a debt of gratitude for that!"
Giggs has played against 117 different teams during his United career.