50 Cent Not Engaged to Cuban Link Despite Huge Diamond Ring

50 Cent and his longtime girlfriend Cuban Link sparked engagement rumors over the weekend after she was spotted wearing a HUGE diamond rock while watching him perform ... but fans shouldn't start cooking up about wedding day scenarios just yet.

A rep for 50 Cent tells TMZ Hip Hop ... the ring is not an engagement ring, but the couple IS very much together.

Cuban certainly helped stir the rumor pot with her IG post showing herself backstage watching her man with a Summer Walker love ballad playing -- plus, her caption had white heart and padlock emojis.

She had to know what fans would think, but again ... we're told there's no engagement.