Rumours about Kaczmarek appearing in the AMC series were fuelled when Breaking Bad star Dean Norris posted an image of himself with the actress and Cranston earlier this month.
Kaczmarek later appeared to confirm the rumours on Twitter, writing: "Yes, it's true... I will indeed be on #BreakingBad. Can't wait for you all to see it."
However, an insider has now told Vulture that Kaczmarek's involvement with Breaking Bad is not actually a role on the television series.
The seven-time Emmy nominee has apparently recorded a featurette with Cranston that will be released on Breaking Bad's upcoming DVD set.
Kaczmarek has not clarified the matter further on her Twitter account.
Cranston and Kaczmarek starred together as married couple Lois and Hal in the sitcom Malcolm in the Middle from 2000 to 2006.
Breaking Bad returns for its final episodes in the summer on AMC.
Watch Bryan Cranston discuss Breaking Bad with Digital Spy below: