We spoke with the former UConn coach who tells us he spoke with Robinson yesterday ... following a medical emergency in Portland earlier this week that left him hospitalized.
Information on Robinson's health has been minimal -- but Calhoun tells TMZ Sports he's confident the 50-year-old is on the road to recovery.
"He's resting and recovering," Calhoun said ... "But he had something sitting on the couch, something happened to him medically. They're working on that now. Yesterday he was on the improvement side, which is great news."
Calhoun wouldn't reveal specifics about what caused Robinson's condition but says, "Very simply, he had a situation that came out of nowhere. For a young man, very unusual."
We asked if the prognosis was good ... he replied, "Yes, it is. But like I said, what he had was very unusual for a young guy."
Get well soon, Cliff.