David's ex-wife, Laurie, left him in 2007, reportedly for Martha's Vineyard contractor Bart Thorpe.
Sources told the New York Post there were "sparks on the set" between David and Landecker when Landecker was a guest star on an August 2010 episode of "Curb."
The Post said David and Landecker first started stepping out in public in February. Journalist Jackson Lynch, Landecker's husband of six years and the father of her daughter, filed for divorce in March.
Although Landecker's publicist told the Post it is "unequivocally not true" David was the reason for the split, Lynch told the newspaper David and Landecker were dating before he filed for divorce.
"This is obviously a sad set of circumstances for our family," Lynch said. "As far we are concerned, it's a private family matter. If you want more details about their relationship you should reach out to Larry."
"For what it's worth, the only marriage I've ever broken up is my own," David said through his publicist to the Post.