"George Clooney didn't want to come on, so that was a bummer," Barr told host Howard Stern.
"I thought, 'Well, he lives in Italy, so...'" she explained.
Clooney played Brooks in the first season of Roseanne, which premiered in 1988. Barr, who voiced her "love" for the actor, recalled how Clooney supported her after she received a chocolate "1" to mark the show's success.
"The show went to No. 1 in its third episode," the actress said. "He goes, 'They [expletive] gave what's-his-face a Rolls Royce on this network.'"
"He goes, 'Let's go out and I'll throw it in there and you hit it with a bat. Then we'll send a picture to the head of the network,'" she recounted.
"I am so greatful to the fans of the Roseanne show for giving it a good Premiere rating," Barr tweeted Wednesday after the revival premiered to 18.2 million viewers. "You are all wonderful-here is to making America laugh & talk again! LOVE U."