The time for speculation is nearly over.
Gatland will announce his squad in London tomorrow and Henry said while the 37 players will be thrilled to make the tour, all of the fixtures will be extremely challenging.
The New Zealander pointed to Wales' morale-sapping 40-7 defeat against the Waikato Chiefs during a tour previous year, when they lost the Test series 3-0.
No wonder the New Zealand-born Gatland has called it the "ultimate test".
Henry points to Wales' match against the Chiefs on their 2016 tour as an example of what the Lions can expect. He has visited New Zealand, scoured the domestic and European club scene, and cast a keen eye on the Six Nations won by England over February-March.
But New Zealand Rugby chief Steve Tew defended it this month, saying it was what the Lions requested. There will be a lot of top-quality players left out by Gatland, sparking uproar throughout the home unions. Warburton, though, is the favorite.
Gatland, who oversaw the 2-1 series victory over Australia four years ago, is tipped to select Welsh flanker Sam Warburton as captain for the second time, an honour previously bestowed only on England's Martin Johnson.
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The tourists are set to face all five New Zealand Super Rugby teams and the Maori All Blacks, as well as three Test matches which are mostly loaded towards the back-end of the trip.
Kruis is expected to be fit again within the next fortnight, and his line-out expertise and exceptional mobility and work-rate means that he could yet claim a place, especially as he will be fresh after a long lay-off.
Warren Gatland is expected to overlook a number of England's Six Nations champions when he names his British & Irish Lions squad on Wednesday, with the second-row Joe Launchbury among those to miss out. However, the streak ended with a 13-9 loss to Ireland on the final weekend of the Six Nations and that Grand Slam-denying result could have consequences.
George Ford, James Haskell and Chris Robshaw are also likely to miss out, according to a report on BBC online, while skipper Dylan Hartley is rated as 50-50.
On the evidence of his Six Nations form it is nearly inconceivable that the powerhouse Welsh captain will not be one of the first names on the lock list, and quite possibly as tour captain. The Lions will likely need to win at least two. They might be hunches. Fellow England teammate of Sinckler, Ben Te'o is also believed to be a lead candidate for one of the five midfield places in the squad. England's Jonathan Joseph scores his third try during the Six Nations rugby union worldwide between England and Scotland at Twickenham stadium in London.
Former Lions and England coach Dick Best is tipping potential British and Irish Lions No 10 Johnny Sexton could struggle to make it through a searching physical examination on the tour of New Zealand.