"He's Losing Blood Badly!"
TMZ has obtained the 911 call made by Oksana Grigorieva -- moments after her teenage son put his hand through a stained glass window in July, slashing his arm wide open.
Oksana screams frantically into the phone, "A huge chunk of meat is missing out of his arm!" 14-year-old Sasha faints in the middle of the phone call.
According to reports, Sasha -- Oksana's son with actor Timothy Dalton -- was treated at a local hospital and released soon after his bloody accident ... but not without several stitches.