James Caan wasted no time ... less than 48 hours after he went to an emergency room, he was back at work, and smiling with his co-star Louis Gossett Jr.
TMZ broke the story ... the 75-year-old showed up to a Toronto hospital Tuesday night for a mild chest infection. He was treated and released, but we were told he'd be unable to return to set for a few days. No rest for the wicked.
Caan and LGJ are filming the family comedy "From Here to Infirmity."