But Grant is still tipped to make his State of Origin starting debut in the Maroons pack ahead of Mahoney in next week's series opener in Townsville after confirming he had overcome a hamstring niggle.
Former Maroons skipper and legendary No.9 Smith - a veteran of a record 42 Origins - raised eyebrows when he overlooked ex-Storm teammate Grant and rated 23-year-old Mahoney as his first-choice Queensland hooker ahead of June 9's Origin I.
Indeed Mahoney has won over plenty of fans in a standout 2021 NRL season, averaging 44 tackles a game to help Parramatta cruise into the top three after 12 rounds.
There was speculation Mahoney had done enough to earn the Maroons No.9 jersey ahead of Grant, who has been sidelined for almost a month due to injury, after both star hookers were named in a 20-strong Queensland squad for next week's interstate series opener.
Even Grant admitted he wouldn't be surprised if he was relegated to the Maroons bench by Mahoney.
Asked what he thought of Smith endorsing Mahoney as Queensland's No.1 hooker, Grant said: "For sure, I think he has been the form hooker all year. "Some of the things that he has been doing in the game not only defensively but also in attack and the minutes he is pumping out, he has had an awesome start to the year."
But Grant still looks set to start for Queensland, filling in for retired Maroons No.9 Jake Friend after making a memorable Origin debut in a series-clinching game three win last year
Still, the Melbourne No.9 hoped he could form a dangerous one-two punch from dummy-half with Mahoney for Queensland, similar to his deadly combination with Storm teammate Brandon Smith in the NRL.
In fact, Grant believed his friendly rivalry with Mahoney in the squad would help him go to another level for the Maroons.
"For sure, we are all in. We are one at the moment. We will do what we can for Queensland," Grant said.
"I am not sure what way (Queensland coach Paul Green) is going to go (for the series opener) but hopefully we can have that combination similar to what me and Brandon have at the Storm."
But Grant backed himself to play a full 80 minutes at No.9 if given the chance by Queensland.
"For sure, I will do whatever it takes. I will back myself physically and mentally to do that (play 80 minutes of Origin)," he said.
"It was touch and go for last week's game (against Brisbane) but given it was a Thursday night it was a bit early in the fixtures so I got a bit of more work done (on his injury).
"It is a bit frustrating but these things happen. I just have to stay on top of it."
Meanwhile, Queensland star Kalyn Ponga said he would make the final call on his fitness ahead of the State of Origin opener after being sidelined for almost a month with a groin complaint.
But the Maroons fullback was "quietly confident" of running out in the series opener.
Grant, Ponga and fellow injury concern Cameron Munster (foot) are not expected to get on the Maroons training paddock until at least Wednesday but must prove their fitness by the weekend according to Green.
"I've got a few boxes to tick," Ponga said.
"I ran on Saturday pretty well so I will give myself every chance to play.
"I think it will be me (to make the final call). At the end of the day it's me playing and I'm the one on the field.
"It's my body at the end of the day and I will know whether I am right.
"Obviously I will have myself in mind but it's team-first mentality but like I said I will put myself in a good position to play."