Van Dijk joined Celtic from Dutch side Groningen in 2013 for around £2.5million and left for Southampton two years later for a reported fee of £13million and during his time in Glasgow he left a huge impression on the Hoops goalkeeper.
Gordon said: "He would be the benchmark for anyone coming through, especially here. When I played with him he was without doubt the best centre-half that I have ever played with.
"He has absolutely everything to go on and become one of the great centre-halves in world football.
"I knew when he left here, I was fairly sure that Southampton wouldn't be his club for very long.
"He is a fantastic footballer and I am sure he is going to do an excellent job for Liverpool. He is a top-class defender, everybody will get to see the best of him now he is playing at a top club."