Players have the ongoing autumn internationals and the Six Nations, as well as club competitions, to show why they should be on the plane.
Who at the moment is performing well? Who needs a run of good matches to seal their spot?
Potentials: Andrew Porter (Ireland), Finlay Bealham (Ireland), Tadhg Furlong (Ireland), Zander Fagerson (Scotland) Will Stuart (England), Ellis Genge (England).
Trending in: Porter.
Trending out: Stuart.
Porter more or less has his name on the team sheet already, barring injury or a dramatic loss of form. He has been a safe pair of hands for Farrell during a golden spell for Ireland. His side may have been beaten by the All Blacks, but the result had little to do with Porter, who showed his immense strength and power.
Another option is Bealham, who has covered the injured Tadgh Furlong, a Farrell mainstay who toured South Africa with the Lions in 2021.
Fagerson is the incumbent in the position having been selected three years ago, so has credit in the bank too.
One player yet to make their mark is Stuart.
Perhaps the spotlight is brighter on the English tighthead given the side's recent struggles, but their scrum hasn't been excellent so far this month. He is yet to properly stake his claim for a Lions spot in this autumn Test series.
Potentials: Ronan Kelleher (Ireland), Dan Sheehan (Ireland), Ewan Ashman (Scotland), Jamie George (England), Dewi Lake (Wales).
Trending in: Kelleher, Ashman.
Trending out: Lake.
There's no doubt George is the best option at the moment for England. His country's recent fortunes and inability to ice games will do him no favours with Farrell but he will surely be on the plane. He could yet be captain, too.
Kelleher has been such a force in Ireland's side it's hard to see him missing out, while Ashman has been showing promising form with the Six Nations still to come.
It leaves Dewi Lake as an outsider, with a decent but unremarkable performance against Fiji last weekend unlikely to cement his place in the side. He will likely need to put on a better show in the months ahead to book his spot.