Conor Murray will have to prove his match fitness before the end of the season or risk missing out on the British & Irish Lions tour.
While the squad is full of power and heft, the decision to pick Jonathan Joseph - who was struggling to make the party - as well as players like Elliot Daly, Stuart Hogg and Liam Williams, means there will be no shortage of pace and skill in the backline.
Hartley's omission makes it the third consecutive Lions tour that will not feature the current England skipper. I was watching the announcement on the TV with the boys and my named got called out.
"I'm so excited and it's reward for all that hard work that people have put into me over the years. I can't tell you how much I'm looking forward to it".
But while the Lions boast impressive depth, Hansen is unconvinced they will bring an expansive approach to their New Zealand games. "In previous tours the midweek games tended to be a little easier, but when you look at the quality of the opposition we're facing in midweek it's going to be hugely challenging", he said.
Hartley led England in 17 Tests during an 18-match unbeaten run that only ended when the team's bid for back-to-back Grand Slams was thwarted by Ireland in Dublin last month. I guess we need to be prepared for what we normally get and prepare for something different as well.
"If someone says 'what do we have to do well to beat the All Blacks?', it's everything", he said.
"I think the fact that me and Tommy are going is down to our team-mates, whether that's at Glasgow or Scotland", Hogg said yesterday.
Sam Warburton, who will captain the Lions for the second time, was also fully aware of the scale of the task ahead.
The gaffe happened when a photograph emerged of Warburton in full Lions kit posing with tour officials.
Warburton, the victorious captain during the 2013 2-1 series win in Australia, is just the second man after England great Martin Johnson (1997 and 2001) to lead the Lions on two tours.
"I wouldn't have been in the right frame of mind but because I do feel I am playing well and I feel very confident about my game at the minute, that is why I said yes".
The tour kicks-off at the Toll Stadium, in Whangarei, on 3 June against the New Zealand Provincial Barbarians.
Gatland's expanded squad takes in 16 English players, 12 Welsh, 11 Irish and two Scottish players.
There is no place for England captain Dylan Hartley, but Wales number eight Ross Moriarty is a surprise inclusion.
Yet there are some significant absentees, the most notable of which sees their captain Hartley overlooked in favour of his global understudy Jamie George, who travels as one of three hookers alongside Rory Best and Ken Owens despite never having started a Test.