Suge Knight is warning Diddy ... he better watch his back in the can, because other inmates are likely plotting against him.
The former Death Row Records exec spoke with NewsNation's "CUOMO" from prison about his longtime rival, saying Diddy has a target on his back.
Suge says prison and jail are inherently dangerous environments for anyone -- famous or not -- and there are inmates in there who want to harm Diddy to make a name for themselves, or prove themselves.
Diddy is being held at the Metropolitan Detention Center in NYC ... long considered a notorious jail, with prisoners living in sickening conditions.
As we've told you ... Diddy was on suicide watch -- a routine measure for new high profile inmates -- but his lawyer said all along Diddy is not suicidal. BTW, we're told he's no longer on suicide watch.
Still, Suge seems to think the extra sets of eyes might not be enough to keep Diddy safe ... but he says Diddy knows what he signed up for.
Suge's an expert on the subject ... dude's been in and out of prison and jail a lot over the past three decades ... currently serving out a 28-year sentence for manslaughter in a California State Prison -- so his warning carries weight.