The Midlanders shipped 17 goals in just four league games over Christmas and New Year, picking up one point from a possible 12.
That has put the performances of the club's defence - and goalkeeper - under intense scrutiny, but Lambert has refused to blame the American.
The Scot has instead suggested things could have been even worse but for Guzan's performances and has backed him to bounce back from recent disappointments.
"I think it might have been harder for Brad if he was a young guy, but Brad is a top professional and really mentally strong," said Lambert.
"From that point of view, yes of course it hurts losing goals, but I don't think it will affect him, not knowing him the way I do.
"I certainly wouldn't put Brad out of the team for what has happened.
"I don't think it's Brad Guzan's fault for the 17 goals we've let in. If it was not for Brad Guzan, it might have been 34."
Lambert has also tipped his other senior goalkeeper, Shay Given, to continue to make an impact at international level.
The 36-year-old announced his retirement from international football following the Republic of Ireland's disastrous Euro 2012 campaign in the summer.
However, reports this week suggest he is ready to reverse that decision and Lambert is in no doubt as to Given's ability to perform for his country.
"If that's Shay's thinking, then fine. For me, the way he's trained and the way he's played in the games has been excellent," added the former Norwich boss.
"He is no doubt good enough to come back and play for Ireland and has played well in the Capital One Cup matches.
"I'm just fortunate to have two such fine keepers available to choose from."