“It’s a huge problem,” Henry told reporters in New Zealnd.
“I don’t think they’ll develop as well in a club environment compared with an international environment.
“The risk they take is that they come back and somebody has established themselves as better than them because they have developed better during that time.”
Henry is speaking in the wake of a New Zealand player exodus that is threatening to grow into a full-scale crisis.
Carl Hayman, Chris Jack, Byron Kelleher, Anton Oliver, Clarke Dermody, Josh Blackie, Sam Tuitupou and Aaron Mauger are all confirmed exits, with a pile of other players set to be about to sign, including young stars like Luke McAlister and Nick Evans, as well as winger Rico Gear.
Henry says this migration will also adversely affect player development in European nations.
“I was told there were only three fly-halves playing in the Premiership who are English,” Henry said.
“I just can’t understand what they’re doing in Europe to develop their own players with all these top players coming from around the world.”