Chris Kattan could barely keep his eyes open filming a recent Food Network show ... and his celebrity co-stars were worried the ex-SNL star was in the throes of a major struggle with addiction.
Kattan was on "Rachael Ray vs. Guy: Celebrity Cook-Off" ... and after nodding off during a meal-planning segment he was booted in the second episode -- which aired last month.
Our on-set sources say Kattan claimed he had been drinking with old "Saturday Night Live" friends the night before and just couldn't stay awake -- but the cast didn't buy it.
Kattan was arrested for DUI this week ... after crashing into a parked car on the freeway. Cops say he admitted to them he had been taking Rx drugs. Hours earlier he was so out of it on an airplane ... paramedics intercepted him when the plane landed.