Boris Becker -- who reportedly made more than $25 MILLION during his tennis career -- was declared bankrupt in a British court hearing early Wednesday morning.

The former #1 ranked player in the world is in the middle of a war with private banking firm Arbuthnot Latham & Co -- which claims Becker has owed them a substantial sum of money dating back to 2015. 

Becker had been fighting back in court trying to get officials to give him a time extension to get his finances in order -- and claimed that he will have millions of euros at is disposal soon after refinancing a property he owns in Spain. 

But the court shot him down saying he'd been delaying too long.

"It is not often the case that a professional person has a judgment outstanding against them since October 2015," the court official said ... "This is a historic debt."

Becker's representative John Briggs begged for mercy ... saying, "He is not a sophisticated individual when it comes to finances.

"I am asking for a real last chance for Mr. Becker to come good ... It has just taken longer than anticipated."