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Kiefer Sutherland didn't just drink while filming -- "24" co-star Giles Matthey says ... he drank BIG ... which is interesting in the wake of Freddie Prinze, Jr.'s recent rant.

Giles played Jordan Reed on the latest season of the hit show and was known to partake in an adult beverage or two (or 3 or 4) with Kiefer. When we caught up to him back in May, Giles said there's no hops or barley on Jack Bauer's party menu -- only WHISKEY.

"No beers for him," Giles tells us.

This comes on the heels of former "24" star Prinze going off on Kiefer yesterday -- as we reported ... Prinze claimed Kiefer would regularly show up on set drunk and was so unprofessional Freddie almost quit acting altogether.

Cool thing is -- this video was shot two months ago, so Giles wasn't reacting to recent events.