Maddison scored the winner in Tottenham’s 1-0 victory over Manchester United on Sunday, just hours after Keane had questioned his impact.
The ex-United captain had claimed the playmaker needed to “step up to the plate” following his injury return, insisting his comeback wouldn’t significantly boost Spurs.
Speaking on the Overlap podcast, he said: "People say Maddison's the man. When is he going to step up to the plate? He got relegated with Leicester and he'll get relegated with Spurs.
"He's good, he's a talented player, but if you're a player in the Spurs dressing room and Maddison's back in the squad, you wouldn't be looking and going 'Oh Jesus, he's back today, we're going to be fine.'"
"Roy Keane's comments were unprovoked," former Aston Villa forward Agbonlahor told talkSPORT.
"Maddison has had a decent season. Can he do better? Yes he can, but these are unprovoked comments.
"I worked with Roy Keane at Aston Villa. I know his character, what he's like, and didn't like it. There’s no need. James Maddison seems like a good lad. Good on him for giving these pundits something back. It just summed Roy Keane up.
"The way the comments were made, it just seemed like it was pre-planned. Let's say something, if it's going to go up on social media it's going to blow up. There’s just no need for it."