Striker Lee Barnard has today moved to League One rivals Southampton for an undisclosed fee.
The Blues forward has joined the Saints ahead of their FA Cup third round clash with Ipswich Town.
And Southend Chairman Ron Martin admitted that he was disappointed to see Barnard go, but that it was in the best interests of all parties to do a deal now than to see United's top scorer leave on a free at the end of the season.
"Nobody will be more disappointed to see Lee Barnard leave than myself," said Mr Martin.
"His contribution this season has been massive but he was out of contract at the end of the season and he would have walked for nothing.
"Had we kept Lee against his wishes it may also have been hard for him to become motivated which we have seen before with players."
Blues had tried on several occasions to negotiate a new deal with the Blues top scorer but were rebuffed in their attempts.
"On a number of occasions, as early as October last year, we tried to open talks about a new contract in recognition of Lee's success but his representatives wished to keep his options open.
"I again tried to pick this up again before Christmas but it was met with the same answer.
"With the real prospect of doubling or trebling his wages at another club is too tempting for a player.
Manager Steve Tilson was equally disappointed to see Barnard leave but understood the decision.
"Lee leaving is disappointing because his goals will be missed," said Tilson.
"But you can understand that a player wants to better himself and the teams that were interested are big draws.
"He's done well for us in the two and a bit years he has been here and we wish him all the best."
However, despite Barnard's departure Southend have already moved to bring in reinforcements.
In a separate deal United have secured the services of Southampton striker Matt Paterson on a free transfer.
Paterson has moved to Roots Hall on a two-and-a-half year deal with an option of a further year.
Blues have also agreed a deal to extend the loan of Wolves left-back Scott Malone until the end of the season and the Chairman confirmed he hoped for another two arrivals shortly.
"We hope to have a permanent centre-back signed before the weekend also" added Mr Martin.
"There is also a possibility of taking a striker on also until the end of the season but that might not happen before the Wycombe match."
