Tendulkar will be retiring from international cricket at the end of his 200th Test, which is currently being played in his home city of Mumbai against the West Indies. (Agencies)
Paying tribute to the 40-year-old, who has been an international cricketer for 24 years, Clarke said he can't really believe that the Indian veteran has grown old.
"It is going to be strange looking at an Indian Test side without the name Sachin Tendulkar sitting proudly in the middle order. He has been the greatest constant in world cricket for a generation," Clarke wrote in his column for 'Daily Telegraph'.
"I was still at primary school when he began his Test career and later scored two centuries on his first tour of Australia as an 18-year-old. I played my first Test series against him almost a decade ago and through my whole career have never really thought about him as an ageing player. I can't believe he is 40," he said.
"I've been lucky enough to play with and against some great batsmen but there have been none better than Sachin in my time. Given everything he has done, Sachin would have to be the second best batsman of all time after the incomparable Bradman."
Clarke said according to him Tendulkar's biggest achievement has been to be an active cricketer for more than 20 years.
"Every time I watch Sachin play he exudes that youthful enthusiasm which highlights just how much he still loves the game, dashing around the field and charging down balls on the boundary," he said.
"So much has been said and written about Sachin's achievements over years. His record number of Test and one-day runs, his century of international centuries. They are achievements that may never be bettered.
"However I believe his greatest achievement is playing international cricket for almost a quarter of a century. That is phenomenal. To be lining up for his 200th Test is mind boggling," he added.
Tendulkar will be retiring from international cricket at the end of his 200th Test, which is currently being played in his home city of Mumbai against the West Indies.