The Lions coaches are using the European semi-final weekend to run the rule over the final few candidates, in much the same way they did on the quarter-final weekend. Gatland took in four games in the quarter-finals and is heading to both Heineken Cup semi-finals this weekend.
He will be joined by Andy Farrell in Montpellier for the game between ASM Clermont Auvergne and Munster Rugby.
On the same day, Rob Howley and Graham Rowntree will be in Dublin watching the Amlin Challenge Cup semi-final between Leinster Rugby and Biarritz Olympique.
All four coaches will then converge on Twickenham for Sunday's Heineken Cup shoot-out. Gatland will announce his squad in London on Tuesday, April 30.
So who will the four Lions coaches be watching? Dublin will give them the chance to assess the fitness of Johnny Sexton and the considerable talent of his understudy, Ian Madigan, for the outside-half berth.
Howley and Rowntree will also run one final check on the fitness and form of Brian O'Driscoll ahead of a possible fourth Lions tour, as well as checking on 2009 Lions Rob Kearney, Jamie Heaslip and Gordon D'Arcy and the likes of first-time tour hopefuls Cian Healy and Sean O'Brien.
The Montpellier match will see Gatland eyeing up players on both sides. Clermont duo Lee Byrne and Nathan Hines were both Lions tourists in 2009, and have been in impressive form for the top-ranked French club, while the fitness and form of Munster's Paul O'Connell might be at the top of the agenda.
Sunday will give all four coaches the chance to watch Jonny Wilkinson in action at his old stamping ground as he tries to guide Toulon into their first Heineken Cup final. Having steered them past Leicester Tigers in the quarter-finals, winning his duel with England outside-half Toby Flood, he will go head-to-head with another England No10 at Twickenham, Owen Farrell.
As well as a host of Saracens players - Chris Ashton, Brad Barritt and Alex Goode - Gatland and co will also be able to assess the suitability of Wilkinson, the Armitage brothers, Nick Kennedy, Simon Shaw, Gethin Jenkins and Andrew Sheridan on the Toulon side.
Shaw, Jenkins and Sheridan all toured with the Lions in South Africa in '05 and '09 (Shaw also toured in 1997) and Jenkins led Wales to the RBS 6 Nations title at the end of the championship.