Brian O’Driscoll would know.
"It's tricky to not play your captain if he's fit, particularly if you are looking at being ready for the England game," he says.
That’s from one Irish captain to another.
Across a mini generation of about seven years, the gulf between the two iconic players is not so vast. Sexton, once fit and healthy, might give Farrell the same look he gave two years ago when he was taken off 10 minutes from the end against France in 2020, if it is suggested he sits out Italy. We will know today.
O'Driscoll would have put up staunch reasons for being picked when he was Irish captain and he believes if Farrell wants to see how Joey Carbery might cope from the beginning this weekend, then the player who occupies the position will not be holding the door open for the Munster outhalf.
Nor will the outside centre in O'Driscoll's old shirt, Garry Ringrose, be inviting Ulster's James Hume into his larder for a raid.
“It’s a tough one,” says O’Driscoll. “I would love to see Joey get a bit more game-time, not necessarily just this weekend, but over the course of the year. They have got to find a way because you cannot rely, going into a World Cup, on a guy of Sexton’s senior years. You just can’t put all your eggs into one basket.
“He has picked up a soft tissue injury last week. It does naturally happen. The older you get, you have more of them.
“We just have to be mindful that we give enough game-time to our perceived second-string players and make sure that they are equipped and ready to go with the necessary game experience to take on World Cup matches.”
But O’Driscoll the pundit is no longer O’Driscoll the player. As a 13, whose position was never threatened, almost throughout his career, there is a striking difference to how both, 43-year-old pundit, 23-year-old player, see it.
The television analyst O’Driscoll sees merit in Farrell’s choice to pick players such as Carbery or Hume as well as others. With a World Cup on the horizon there has to be realistic squad depth. But as a competitive and ambitious back, it is not something he would have personally entertained.
“The player is always going to put themselves first in the pecking order, try to get the coach to select them,” he says. “The last thing you want to do is ever give an opportunity to somebody else. Unless you have total comfort and you are the number one, even still, to give someone the chance to impress, to get game time under their belt is never a nice feeling.
“I wouldn’t imagine Garry Ringrose is going to be encouraging James Hume into the team at any point. He might be generous at training and share his knowledge. But ultimately I think he’ll be trying to hold on to the 13 jersey for as many Test matches in a row as he can to cement his position as the number one and not give any incumbent an opportunity to impress the coach.”
Italy are one of the teams that give Ireland some limited experimental opportunity that sides such as France and England do not. Ireland's reliance on the Six Nations to compete well and maintain interest has always been wrapped up in the financial prudence of the IRFU and competition. It is Irish rugby's cash cow.
But the other imperative has to be looking beyond centre Bundee Aki, Robbie Henshaw and Ringrose; looking beyond fullback Hugo Keenan and at Mack Hansen or Michael Lowry, who also sees himself as an outhalf; looking beyond Sexton and Tadhg Furlong and Andrew Porter. Would O'Driscoll the pundit, not the player, make changes for Italy?
"I would to be honest with you," he says. "This is one of the few Six Nations games where you feel as though you can have the ability to change things up and take whatever Italy throws at you, particularly playing at home.
“So I do feel as though you could throw three or four players in there and not lose a huge amount and give invaluable game time to those players and a confidence boost for them. We are all confidence players and particularly if you perform well it gives you confidence. It also gives the coaching ticket the confidence to be able to rely on you.”
The outhalf issue, he says, revolves around whether Farrell wants to bring two or three to France for the 2023 World Cup. Time wise, Farrell doesn’t really have that much, to properly bed in another player such as Carbery, a player who with secured game time would not be seen to weaken the team if Sexton were injured.
With a tour to New Zealand this summer and internationals in the autumn as well as the 2023 Six Nations, there is not much wriggle room to stack up the caps for non-starting players.
"Conor Murray is another who could potentially fill in at outhalf] and play against an opposition if push came to shove, so whether there is enough confidence . . ." says O'Driscoll, who is speaking as a Guinness Ambassador.
“In most times you only want to be carrying two [outhalves] but with the reality that Johnny is a little bit older maybe you have to err on the side of caution and bring a third one. It just depends on who that is.
“Is it an out-and-out 10? Does he see Joey as being a viable 15 option as well, which covers a few positions, and let Johnny and Jack [Carty] be the out-and-out 10s?”
The beauty now of New Zealand this summer is Sexton could travel, play one match or two and then come home and maintain the balancing act between game time and possible injury. So far in the Six Nations, he has shown more than ever how pivotal he remains.
“I don’t know whether Johnny will travel down there. Maybe he’ll get two or three Tests,” says O’Driscoll. “But I think over the course of the coming months, he [Carbery] needs more starts.
“I would definitely encourage that Joey does get more game-time and maybe the time for him will be down in New Zealand.”
For now, it is Italy and a Farrell tapestry of players or an artisan drive for Six Nations table position.