Rice earned rave reviews for his performances for the Hammers at the start of the season, forcing his way into the England squad, and talk soon turned to how far he could go in the game.
Rumours also started linking him with a big-money move to the likes of Manchester United and Manchester City, but the honeymoon period now looks to be over.
The youngster's performances have dipped for West Ham, and although he played the full 90 minutes for England against Kosovo on Sunday night, he had been dropped for the previous two international games.
Keane believes that is because his performances have been below par of late, and he did not hold back when asked about the deficiencies in his game.
Keane coached Rice who part of the Republic of Ireland set up, before he switched allegiance to England, and says there is plenty he needs to work before he can call himself the complete player.
"Where he needs to improve, there are plenty of aspects if you think about it," he said on ITV Sport.
"Over the last few months he has had a lot of praise, I worked with him while he was with the Ireland squad.
"Where does he need to improve, where do you want me to start? His positional play I don't think is consistent enough, he doesn't stay with runners, he's sloppy in possession. I can go on."
The comments appear to be harsh and could be down to the fact Rice angered many in the Republic camp with his decision to play for England instead.
He is also only 21 and there is time for him to work on and improve on the deficiencies that may be in his game.