The 27-year-old former Celtic midfielder believes that Forrest could leave the Hoops in the summer transfer window and play for any club in the world.
Slane has also suggested that the 27-year-old Scotland international winger is good enough to replace Ousmane Dembele at Barcelona.
The 22-year-old France international forward missed a glorious chance to make it 4-0 to Barcelona in the first leg of their Champions League semi-final tie against Liverpool at Anfield this month.
That miss came back to haunt the Spanish and European giants, as Liverpool won the second led 4-0 at Anfield to progress to the final 4-3 on aggregate.
Dembele, who had had injury problems over the past two years, has been on the books of Barcelona since the summer of 2017 when he joined from German club Borussia Dortmund for an initial transfer fee reported by BBC Sport to be worth £96.8 million.
Slane said about Forrest on Open Goal: “I am petrified because I don’t think he is going to be here. He is going to be at one of the biggest clubs in the world next season.
"I think that if he is, you know name, Barcelona 4-0 v Liverpool, who is playing it there? Dembele? An embarrassment playing with Barcelona. I would say Forrest could go to any club, he is that good.”
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