"Juror #2," out Friday, is a suspenseful courtroom drama in which a jury member discovers he may be personally connected to a high-profile murder trial.
It stars Nicholas Hoult, Toni Collette and J.K. Simmons, as well as Eastwood's daughter Francesca.
"It was very special to be working with such an icon as Clint Eastwood," said Hoult. "Obviously terrifying but... he has a cracking sense of humor and charm."
"He's a truly good, solid human being," added Collette.
The movie has received strong reviews. Deadline called it Eastwood's "best since 'American Sniper,'" and "one of the most compelling human dramas of his career."
But Eastwood was glaringly absent from the film's glitzy premiere at the annual AFI Fest in Hollywood on Sunday night.
Days earlier, trade publication Variety had reported that studio Warner Bros was "burying" the film, by releasing it in fewer than 50 theaters -- an unusually limited number for the major Hollywood studio.
Eastwood's previous film "Cry Macho," also released by Warner Bros, was a box office flop.
The Variety report has led fans to speculate on a rift between Warner Bros and Eastwood.
Representatives for the studio and director did not immediately respond to AFP request for comment.
"I know he's very sad not to be here tonight," said Hoult, without providing further details.
Speculation has also swirled over the nonagenarian's health, particularly since the death of his long-term partner Christina Sandera in July -- though Eastwood has shown few signs of slowing his prodigious film output.
The multiple Oscar-winning actor-turned-director, born in 1930, churned out nine films in his 80s, and "Juror #2" is the second film he has directed in his 90s.
As well as Oscars for "Unforgiven" and "Million Dollar Baby," he earned a lifetime achievement Palme d'Or from the Cannes festival.
In interviews, he has spoken of his desire to keep working as long as he finds projects that are "worth studying."
Co-star Cedric Yarbrough told AFP that during the filming of "Juror #2," Eastwood had personally apologized to individual drivers who were held up when a road was blocked off to shoot a scene.
"As an actor, I love watching someone like him, with that kind of status, enjoying the process and being kind to other folks," he said.
"It's classy, it's old Hollywood. It's what you want to see in your icons. That's the boss."
