Former NBA star Paul Pierce detailed his dire financial situation in court ... claiming he only has a couple grand left each month after paying his bills, TMZ has learned. 

According to court docs obtained by TMZ, Paul says he only has around $3,793 per month ... after paying his court-ordered child and spousal support, which totals $48K per month. 

The Truth says he was earning an average of $138K per month before he lost his Fox Sports gig. He says he earned around $10K from YouTube for the year and was paid over $60K from Fanatics.

Paul says his remaining income "is sufficient to satisfy his existing support obligations."

He points out his ex, Princess Santiago, is currently making $0 per month despite her being a major money maker. 

As TMZ first reported, Paul is fighting Princess’s request for another $40K to cover legal fees and $10K to hire a forensic accountant to review the ex-NBA star's finances. 

Paul claims he is not making money like he did when he was in the NBA or even when he had a job on Fox Sports ... claiming he is struggling to stay afloat ... despite reportedly making over $200 million during his time in the league. 

 As TMZ first reported, Paul was ordered to pay $8K per month in temporary child support ... and another $100K to pay Princess's legal bills.