Hard to say, I haven't seen much video of him ,Cerdan did have wins over Tony Zale and Holman Williams who I think are 2 better wins than any Golovkin had at 160 and he was a very active fighter. I'd have loved to see how his rematch with LaMotta had went as I believe he'd have won. If Cerdan could slip GGG's jab and get inside he could take a decision, assuming he could take GGG's power
What I have seen of Cerdan makes me think that he was an excellent fighter but I don't think he has it to beat Golovkin. Maybe if he was in top form and he got the influenza version GGG. All things equal I think GGG has too many arrows in his quiver.
Cerdan is a light- welterweight now. He is 5’6 going by memory. Golovkin would knock him out inside six for me.
