Rival IBM, on the other hand, divested PCs and servers years ago on the realization these businesses have little growth potential, McNamee said.
"In fairness, I think HP has been horribly managed for 20 years and, you know, so [CEO] Meg Whitman didn't inherit a great situation, but I don't think there's any evidence that she's gotten control of it, that she has any idea what they ought to do next," he said. "I don't see any plan for either side of these things that's going to make a difference to shareholders ... the long-term outlook for both sides of this business is terrible."
Read MoreThe benefits and pitfalls of breakup at HP
Earlier, Hewlett-Packard surged after saying it would split its hardware and services businesses from the personal-computer and printer business, forming two publicly traded companies.
"We think this is the best tactic to continue this turnaround journey and position HP into two great new companies that are real scale and have a real chance to make a real difference on a go-forward business," Whitman said on "Squawk on the Street."
"We're really excited about this," she said. "I think it's going to be better offerings for customers and partners, career opportunities for employees and we believe it will create real shareholder value."