Alonso believes Gerrard had a significant impact on his career, having moved to Merseyside from Real Sociedad in 2004.
"He was a great influence to me," he told Real Madrid TV in an interview on behalf of Liverpoolfc.com.
"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 team-mates 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."