Chief Keef -- Another Day, Another Baby

Chief Keef just learned he's a daddy ... again ... bad news for him because he now owes another big chunk of change for child support ... TMZ has learned.

Keef's attorney says the rapper admitted he's the father of a 10-month old child ... after being confronted with some pretty conclusive evidence -- his own DNA.

According to the lawyer ... Erica Early went to court in Chicago to establish paternity. The DNA test shows there's a 99.9% chance Keef is the papa.

The 18-year-old rapper is still in court-ordered rehab in California for his weed smoking ... so he wasn't in court when the judge ordered him to pay Early $2,500 a month in child support ... plus, another $25K lump sum payment for the previous 10 months.

But good luck collecting ... Keef owes thousands of dollars in back child support in ANOTHER paternity case ... and he's not coughing it up willingly.