Scott Disick -- Friends Pushing Him to Rehab, Stat!

Kourtney Kardashian's not the only one fed up with Scott Disick -- on the heels of missing his daughter's 3rd birthday, friends are urgently trying to get him into rehab.

Sources tell us Kourtney was peeved about Disick missing Penelope's party at Disneyland on Wednesday, and she was told some of Disick's pals feel it's more evidence he's off the wagon again.

We're told they've been trying to convince him to get treatment -- even before the bday screw up -- and they think they're on a deadline. Scott's scheduled to host a party Friday night at 1Oak in Las Vegas ... which the friends think is a dire mistake.

Our sources say they want him to cancel the appearance and get into a treatment program instead.

Stay tuned ...