The 24-year-old made his competitive debut on Sunday as Arsenal defeated Manchester City on penalties to win the Community Shield following a 1-1 draw in regulation time.
Asked about the midfielder’s prospects in North London ahead of the game, Keane told ITV1: “He is obviously going to be surrounded by better players, different demands.
“If he is going to play a little higher up the pitch, I think he definitely has that quality in terms of adding more goals. He’s obviously got that physical strength, he can get in the box.
“They have obviously paid way too much for him. He’s certainly not worth over £100 million, Declan Rice, but a really good player.
“We’ll find out over the next year or two how good Declan is. He turns up every week, he is a big strong boy – again, you talk about that physicality, they lacked that in the last month or two (of last season).
“Has he got that really top quality in terms of seeing a pass and getting nine, 10 goals? We’ll soon find out.”
Rice captained West Ham to Europa Conference League glory in June before leaving for the Gunners.
