The move – estimated to be a €600,000 three-year deal for McCarthy – has seen the western minnows lose their best player this season to the eastern giants.
A clearly unhappy Connacht CEO, Tom Sears, issued a carefully worded statement in which he took a swipe at Leinster for "persistently targeting Connacht players in recent years" and also questioned if Irish rugby would ultimately be the loser.
While Leinster have remained silent on the issue, their supporters will be sure to point out that McCarthy was being offered the same figure by both sides and it was the player who ultimately made the decision to move.
Sears, however, was quick to argue that similar transfers have not always been successful.
"Fionn Carr, for example, was one of the leading try scorers in the Celtic League with Connacht. How much rugby is he playing with Leinster?" asked Sears.
"The likes of Fionn and Jamie Hagan would certainly be playing more rugby were they still Connacht players.
"We wish those players all the best when they leave us, but how it is beneficial to go from playing regularly to not?
"We have been aware of Leinster's interest in Mike for some time. It is disappointing they have persistently targeted Connacht players in recent years, particularly when often not in the best interest of Irish rugby."
Sears remains bullish, however, about Connacht's future development and progress.
"We won't adopt a defeatist attitude and wail and moan about the situation.
"We will continue to strive to prove to players that they can fulfil their potential with Connacht and win trophies as Connacht players.
Connacht are caught helplessly on the horns of a dilemma. They must help the players on their roster develop their skills to international level if they are to compete at the level they aspire to.
They do so in the certain knowledge that as soon as any one of their players achieves a level of prominence then he will be courted by the bigger and more successful clubs, not only in Ireland, but across Europe.