Press Association Sport understands that fly-half Wilkinson will miss out on selection when Lions head coach Warren Gatland names his 38-man group on Tuesday morning. Jonathan Sexton and Owen Farrell are believed to be Gatland's chosen ones at number 10.
"Even if they (Lions) don't see him as the best number 10, I just think there is so much he can add to the group," said former Australia Test star Giteau.
"Games like a Heineken semi-final (Wilkinson kicked 24 points in the win over Saracens) are quite similar to Test matches, with the physicality and tempo of the game.
"It's almost like a chess game. You have got to take your points when they are on offer, play field position, play smart.
"Jonny looks after himself. I have worked and played with a lot of great players, and not taking anything away from their work ethic, but no-one works harder than Jonny.
"He is a perfectionist, he is in the game for the right reasons, and while he still loves the game he puts performances like that on the field."
Giteau played a part in 33-year-old Wilkinson recently choosing to extend his stay at Toulon into next season, adding: "Jonny's biggest fear was that he felt he was holding the group back, so I made it quite clear and told him that my rugby was improving and other guys around us as well.
"And while it was like that, he was still adding to the group. I just convinced him of it. As far as rugby goes, Jonny Wilkinson is right up there as one of the greats who has played the game.
"I want to hate the guy! He has knocked Australia out of two World Cups, but he is just too nice. It would be great for Australia as well if he went on the Lions tour, they would love to see him go back. You have got to respect him for what he's done, and Australia certainly isn't bitter in that way."
- Sports & Recreation
- Warren Gatland
- Jonny Wilkinson