11/10/2012 at 01:50 PM EST
Weight-wise, Matthew McConaughey
is at his lowest point.
The actor, 43, was snapped looking shockingly frail Friday as he caught a flight from Los Angeles to New Orleans, where The Dallas Buyer's Club
is set to begin filming Sunday.
McConaughey has lost 30 lbs.
– and gained a mustache – for the role. In the movie, he plays a mid-1980s AIDS patient
who seeks out experimental HIV drugs to prolong his life.
"Matthew starts shooting this weekend, so he's at his absolute lowest weight," a source close to the actor tells PEOPLE. "In a month, he'll begin to put it back on."
Around the time he gains the weight back, McConaughey will gain a new family member
as well – wife Camila
is set to deliver
their third child this winter
Reporting by ELIZABETH LEONARD