Liverpool-owned ace Grujic spent a portion of last season on loan in South Wales, helping the Bluebirds gain promotion to the Premier League.
The 23-year-old revealed what it was like to play under Warnock - and told the story of his first meeting with the veteran boss.
“It was a good experience for me to work under him," he told Goal. “He's really popular with the players, a very funny guy who knows how to motivate people.
“For me, I needed someone like him at that point in my career. Before every game, he focuses a lot on defending and that's how I look at football as well. If you defend well, then you will always have a chance even against a good team.
“My first meetings before I signed, he was very funny. I met him in the stadium and he told me I was bigger than I sounded on the phone! He spoke a lot with me and my father as well, and told me immediately that I would play. He's a direct guy, says what he thinks.
“What he did with us in the Championship was great. We were not expected to get promoted but he got us playing to a specific style and it worked.
“And then look at this season. Look at a team like Fulham, who spent much more money than Cardiff but got nothing to show for it.
“Cardiff still have a chance to stay in the league, and I am really hoping they can do so because it's a great club and I really enjoyed my time there. I will be interested to see the result."