After a sustained dip in form, the 26-year-old called an emotional end to a seven-years Spurs career by joining Everton on an initial free transfer, with add-ons to come should certain performance-based criteria be met.
Still, the former England international failed to settle at Goodison Park, making only one Premier League start while on Merseyside.
As a result, Dele was allowed to join Turkish Super Lig giants Besiktas on a free transfer during the summer transfer window. On Sunday, he scored his first goal for the club in a 3-2 win over Ankaragucu.
Speaking to talkSPORT, former Spurs boss Redknapp said: “I called Frank and said, ‘take the chance on Dele Alli. He’s got fantastic ability and you can get him going’.
“Going to a big club like Everton could give him a big lift and Frank said he was down the road already and I said, ‘brilliant, I think he’ll be great for you’.
“He was a disaster, a disaster. I watched him play and he loses the ball, he walks and doesn’t run, I don’t know what’s happened to him.”