The midfielder, with his deal running down, is enjoying career best form this season.
Symons worked with Wilson for both Wales and Fulham and told talkSPORT: "Harry has become the player everyone always hoped and envisaged he would be.
“He always had the quality.
“I was first aware of him during a meeting at the Vale Hotel outside Cardiff when the Wales Under-21s manager Geraint Williams said, ‘You have to pick this kid.’
“There had been talk of England being keen so Chris (Coleman) picked him for the first team.
“You never know how players will turn out but there is nothing worse in football than unfulfilled potential.
“So it’s great to see him performing so well.
“He has a wand of a left foot, we saw that in training straight away.
“And he would practise after training, especially on his free-kicks. It’s no surprise to see how many great goals he scores now.
“Since Gareth (Bale) retired for Wales, Harry’s shown form.
“He’s stepped up and not everyone thought it would be him – many believed it would be Brennan Johnson.
“But he’s been brilliant and he has taken that that has into his club performances. He has become Fulham’s most important player.”