The Argentine moved to Tottenham this week.
"It's a blow for everybody to lose him, you can't really get away from that, and the players all loved working for him," said the Northern Ireland captain.
"He pushed us on from where we were at before he came in; everyone personally improved, results improved as well and things were looking bright for the future.
"It's disappointing but at the same time I don't think it will affect the club in terms of progression because there is still a lot of growth left in the team.
"The club has come a long way in the last five years and the blueprint has been evident under each and every manager.
"There is no reason why that should stop now and everyone will want to get going forward to achieve our goals."
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