Lambert, whose Midlands strugglers face the Black Cats in a crunch relegation scrap tomorrow, admits to being appalled at the criticism levelled at his former Celtic manager.
The Scot, 43, said: "It's shocking. It's awful to hear some of these things being said - and it's probably people who haven't been a manager who are calling him these things.
"Listen, I worked under Martin at Celtic for five years and he was breath of fresh air up there. He was absolutely brilliant. He took Celtic by the scruff of the neck when it was dead on its knees and got us to a European final and winning trophies again.
"I've spoken to Martin since he left Sunderland and he's fine. And I am sure he will be back in the game soon."