King, who was replaced by Morgan on CNN, told BBC Radio 4's PM that he believes network executives made an error in the way they marketed Piers Morgan Tonight.
"I think one of the problems they did was over-sell it," he said. "He was going to be dangerous, he was going to be water cooler talk."
King added: "He's good but not that dangerous. I think they might have been better off starting quietly and that's not Piers' fault, or maybe it is - I'm not inside anymore."
The 77-year-old broadcaster went on to say that he believes Morgan can be successful in the prime-time slot if he is given the chance to grow an audience over time.
"He's certainly not bad. He's certainly an acceptable host," he said. "He asks good questions... maybe he interrupts a little too much at times. I [just] think he may have been oversold."
King hosted a talkshow on CNN for more than 25 years before leaving the network in December 2010.
