Kevin Federline has been generous these past couple of weeks with deposition subpoenas for various people in Britney Spears’ entourage. Now he is fishing for bigger fish: Britney’s rehab records at Promises.

The 29-year-old former Mr. Britney Spears wants sole custody of sons Sean Preston and Jayden James and he is determined to prove that his former missus is no fit mother.

After serving legal papers to Britney’s former personal assistant, former bodyguard and current personal assistant, K-Fed’s lawyer handed a deposition subpoena to a chief administrator at the Promises rehabilitation facility in Malibu.

It was Mark Vincent Kaplan, Federline’s attorney, who announced this move Sunday. He said the chief administrator had received his subpoena Saturday. Britney spent several weeks at Promises earlier this year, after her notorious self-applied haircut in front of the paparazzi and several other incidents.

All those served with legal papers by Federline’s legal team will testify in court as to Britney’s parenting skills and lifestyle.

Former assistant Shannon Funk, 21, will probably be questioned about a rumored affair between the “Toxic” singer and herself.

It remains to be seen whether the judge handling the custody case will accept a testimony from the Promises employee, considering that there is a confidentiality clause that patients benefit from.

“They are pursuing all relevant evidence from every potential source and every available witness, including witnesses who might actually believe they could succeed in becoming unavailable,” a source told “Access Hollywood,” referring to Kevin Federline’s legal team.

Among those subpoenaed are former bodyguard and driver Daimon Shippen and current assistant and cousin Alli Sims.

It has been reported that Britney and her mother, Lynne Spears, had a falling out earlier this year and as a result, Mrs. Spears has chosen to support her former son-in-law in the custody battle. Britney and her mom are reportedly no longer on speaking terms.

To make matters even worse, the singer’s renowned lawyer, Laura Wasser, is reportedly leaving her client. Britney was photographed earlier this week as she left her lawyer’s office and she was crying.

Interestingly enough, Federline, 29, has two other children with Shar Jackson. She was allegedly pregnant with their second child when Federline, then a back-up dancer for Britney, started his relationship with the pop singer.

Has he made a big big fuss about obtaining custody for those two kids?

One way or another, the less famous mother of his two other children seems to bear him no grudge. On the contrary. TMZ.com reports that Shar Jackson recently declared, “Kevin is a great dad!”