The 25-year-old was offloaded by Tottenham in the January transfer window after successive managers in north London had failed to spark Alli back to life.
He is still struggling at Everton and boss Frank Lampard regularly prefers other players in his starting eleven, something which has raised further questions on whether Alli can return to his best.
However, Roberts still has full faith in the England international and feels that he needs to be given full support in his attempt to come out of the rough patch.
“I do believe there is still a special talent there and rather than kick a man when he is down people should be supporting the lad”, Roberts wrote on Twitter.
Alli was greeted by the fans when he visited the Tottenham Hotspur Stadium in early March.
Urging Alli to prove his doubters wrong, Roberts added: “You saw what he meant to the Spurs fans a few weeks ago when he came back to Tottenham. Dele you can do it mate go prove people wrong.
“People all having a go at Alli in the media and on tv you are all talking about him because he was such a wonderful player for Spurs and now easy to put him down.
“Let’s try to encourage him to get back to near what he was.
“He may be going through things away from football.”
Everton paid no initial fee for Alli, but Tottenham are in line to recoup millions if he hits a number of targets on Merseyside.
