Genia only returned to action last month following a nasty knee injury that ruled him out of much of the Rugby Championship and the entire end-of-year tour but he has since been in sparkling form for the high-flying Reds.
The 25-year-old is a near certain starter for the Aussies in Brisbane, Melbourne and Sydney and Gatland expects him to replicate his club form for his country when the Lions come calling.
"Will Genia is the best nine in world rugby," said Gatland.
"I think for a man still young, he is very experienced and he is a real talisman for Australian rugby.
"When he is playing well, Australia or the Reds play well and you see that at the moment.
"It is great to see him back on the field, and he is making a really significant impact. He is competitive, he is an intelligent rugby player and he is someone we are going to have to limit.
"When he is in form and he is controlling the game he has a massive impact on the field."
Gatland also expects to encounter Genia's Reds halfback partner Quade Cooper in the three-match Test series, even though the controversial playmaker missed out on selection for a recent Wallaby training camp.
Cooper was overlooked by Wallaby boss Robbie Deans for his latest gathering but has responded in the perfect manner by shining repeatedly in the Super XV.
Genia has spoken of his desire to play alongside his club colleague in Australian colours once more and Gatland believes that wish is likely to be granted at the Suncorp Stadium on June 22.
The same goes for fellow star Kurtley Beale who, like Cooper, fell foul of the authorities and is currently suspended for an off-field incident in which he allegedly struck a team-mate on the Rebels' recent tour of South Africa.
"From an Australian point of view, I don't see how they can afford to leave someone of the quality of Quade Cooper out of the team," added Gatland.
"And they have got the same issues with Kurtley Beale as well. From my aspect it seems there are a number of off-field issues that need to be sorted with players before they are thinking about playing rugby on the field."