The Republic of Ireland striker was sold by Spurs, then managed by Ramos, in the summer for £20 million. But he lasted just six months - scoring seven goals - before hot-footing it back to north London, leaving the Reds in the red from the overall deal.
And Ramos, who was sacked at White Hart Lane months after seeing prize assets Keane and Dimitar Berbatov sold, now believes Liverpool's decision to sell Keane so quickly will cost them when they meet Ramos's Real Madrid in the Champions League last 16.
"You can't tell me Robbie will not score goals at a top club," Ramos told The Sun. "He is a top player and I don't think he did badly at Liverpool. He scored goals and showed he's a team player.
"He's definitely a match-winner for any club and if he were still at Liverpool, I would be telling my defenders to watch for him.
"When you are a top club playing around 60 matches a season, you don't want to let any of your players go in January unless they have a real desire to go.
"It was a lot of money to lose on Robbie over such a short space of time, especially in this market. Let's put it this way. I wouldn't want to lose that amount of money on one player.
"Maybe Liverpool should have kept Robbie until at least the summer to give him more time and try and get the right price for him when there was more time to do so."
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