Veteran captain Sexton has been a mainstay in his country’s number 10 jersey for more than a decade and is poised to win his 100th cap when Japan visit Dublin on Saturday afternoon.
Joey Carbery who has been named among the replacements, and Harry Byrne are the alternative fly-halves in the current Irish squad, while Jack Carty and Billy Burns were overlooked for the autumn campaign.
Leinster player Sexton will be 38 by the time of the 2023 World Cup in France but Farrell insists he has no concerns about the experienced Leinster player still being first choice.
“It’s certainly not a worry,” Farrell said of competition for the role. “Johnny is a world-class player so why would I worry about that?
“Johnny isn’t just going to stand to the side and say, ‘there you go guys, off you go and take over now’. We want those guys and other 10s to challenge Johnny and knock him off his perch.
“You don’t want to just hand something over to someone that doesn’t deserve it. That’s not a squad.”
Sexton will become the seventh Irishman to reach a century of Ireland caps following Brian O’Driscoll, Ronan O’Gara, Rory Best, Cian Healy, Paul O’Connell and John Hayes.
He was rested for the summer Tests against Japan and the United States, allowing Munster’s Carbery to make his first national team appearances since the 2019 World Cup following a tough period of injury problems.
Connacht player Carty has not featured at international level for more than two years, while Leinster fly-half Byrne and Ulster’s Burns have made just two Test starts combined.
Farrell believes Carbery and Byrne are eager to develop at international level.
He said: “What do we want to see from Joey and Harry? We want to see them pushing Johnny. They love the honest feedback and that’s how we are with them.
“They want to know how they can improve and what they have to do to improve. A lot of the time at this level because of the speed and intensity of training, it’s the calmness of thought in that type of position.
“Learning to deal with that, with the pressure of trying to understand how best you can get prepared in such a short space of time, it’s daunting enough.”
Farrell has named a strong starting XV for the weekend clash with the Brave Blossoms.
British and Irish Lions quartet Tadhg Furlong, Tadhg Beirne, Jack Conan and Bundee Aki are among those to return, while replacement hooker Dan Sheehan is the only potential debutant.
James Lowe has also been recalled after being dropped for the Guinness Six Nations finale against England in March and then missing out in the summer due to injury.
Farrell has backed the New Zealand-born winger to prove his worth.
“I have been impressed with how he has gone about dealing with the tough time that he went through,” Farrell said of Lowe.
“He has had a good look at himself with regards to his preparation and I think it was a little bit of a shock for him first time up with the pressures and the scrutiny of international rugby.
“He has gone away, been very diligent and wanted to work on aspects of his game that we have asked him to, and there are improvements there.
“He gets his chance because of all that, to show us that he is the right man for the job. He is in great nick, he has lost a bit of weight, he has the bit between his teeth.”
Munster forward Gavin Coombes, who made his debut in the summer, was ruled out of the game due to a non-coronavirus illness.
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