Recent squad announcements have come after the Champions Cup semi-finals, but has been brought forward this year to April 19.
This weekend sees Leinster, Wasps, Munster, Saracens and Glasgow all in action in the quarter-finals.
Who could make a lasting impression on Gantland? We take a look at the options.
Danny Cipriani, fly-half (Wasps)
A long shot for the tour, but Gatland has already spoken to Cipriani about Lions selection even though he has not started for England since 2008.
The two worked together at Wasps and Cipriani offers something slightly different to the fly-halves who played in the Six Nations.
A strong performance against Leinster's Johnny Sexton - the Lions' current first choice at 10 - would advance his claim.
Jamie George, hooker (Saracens)
Hooker is one of the trickiest positions, not least because of England's pecking order.
George is the Aviva Premiership's form player in the number two jersey, yet he plays second fiddle to Dylan Hartley for the Six Nations champions.
He is also forced to content himself with second-half cameos off the bench, during which he has excelled.
Saracens' quarter-final against Glasgow is a chance for George to shine right from the start.
Peter O'Mahony, back row (Munster)
A mighty roar greeted the announcement shortly before kick-off that O'Mahony would replace Jamie Heaslip for Ireland's clash with England.
Over the next 80 minutes the Munster flanker justified the Aviva Stadium's approval with a man of the match display.
His frenzied all-out commitment and line-out expertise would make him a valuable tourist, a point he can emphasise against Toulouse.
Sean O'Brien, back row (Leinster)
Injuries have taken their toll on Leinster's rampaging back row, but O'Brien remains a force with his physicality, ball-carrying and breakdown work placing him in the mix for the Lions' back row.
It is one of the most competitive areas in the squad, not least because the abundance of riches at lock could see the likes of Maro Itoje and Iain Henderson come into contention.
But a successful duel with Wasps' James Haskell will elevate his cause in Gatland's eyes.
Finn Russell, fly-half (Glasgow)
Russell has been a revelation for Scotland, his creativity and willingness to take risks a factor behind a strong Six Nations for Vern Cotter's men.
But how much will the team's collapse against England at Twickenham have affected his chances? It was a big occasion and to a man Scotland failed to turn up.
Sexton, George Ford, Owen Farrell and Dan Biggar are also in the mix at fly-half, although Gatland may view Farrell - Russell's opposite number on Sunday - as an inside centre.