The singer, 26, lost her rights to see Jayden James, 1, and Sean Preston, 2, in January. Ex hubby Kevin Kederline, 29, currently has full custody.
But Jason - whose marriage to the singer lasted just 55 hours after their Vegas wedding 4 years ago - says she's not bothered about getting them back.
'She wants to see the kids, but she doesn't want to be a full-time mum,' he says.
'She said that it doesn't matter if she doesn't get them back full time, and that she can always have other kids later on.
'I don't think she should have full custody because she needs to focus on herself.'
Jason lost touch with Brit after their brief marriage, but they now chat every day.
'As I friend who loves Britney I worry about her. She seems to have lost touch with reality and lost sight of what's really important in life,' he tells The Sun.
'I keep crossing my fingers and hoping that nothing really bad happens to her.'
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