The Spaniard played alongside the England skipper for five years at Anfield before opting to move to the La Liga champions in 2009.
Alonso has since gone on to win two European Championships and a World Cup with Spain, and says that he learned a lot from Gerrard from his time on Merseyside.
"He was a great influence to me," said Alonso. "When I arrived at Liverpool I was 22 and he was the captain, he was the main man at the club.
"For me he was a reference, the way he behaved with his teammates and with the supporters as well. I learned a lot from him. We are great friends and we still keep in touch.
"He is so inspirational. In the key moments he has that different thing, that spark that is difficult to define. He'll absolutely be remembered as one of the greats. For me he is already one of the greats."
Alonso has over 100 caps for Spain.