Keane lasted just six months at Anfield following his £20million move before Liverpool agreed to sell him back to Tottenham for a loss on their initial outlay.
Ramos was reluctant to lose Keane to Liverpool while he was in charge of Tottenham and he admits he was surprised to see Benitez offload the Irishman after such a short spell on Merseyside.
"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."
GambleRamos also admitted Benitez has taken a massive gamble by letting Keane go in the January transfer window without bringing in a replacement.
"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," added Ramos.
"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!"