Johan Renck doesn't think 'Spaceman' could exist without Adam Sandler's "formidable and amazing" performance.

The Swedish director cast the 'Happy Gilmore' star as lonely Czech cosmonaut Jakub, who befriends a giant telepathic space spider while on a solo mission in his new movie - which is adapted from Jaroslav Kalfar’s novel 'Spaceman of Bohemia' - and while he found much of making the film to be a "frustrating" experience, his leading man's work made it all worthwhile.

Johan told The Hollywood Reporter: "When I look at this film now and I look at Adam’s performance, it’s phenomenal. He was hanging there on the wires. And he’s no spring chicken anymore. He’s not a gymnast or a bodybuilder.

"And he’s hanging in mid-air, acting against a tennis ball, with me around the corner reading lines.

"Then you look at the film and see the profound curiosity in his eyes, the bafflement, all these subtle details. All this acting against a tennis ball.

"I would come home every day after the shoot, feeling tremendously frustrated because I only had one-half of the movie. It took months and months as we created the creature, did the voice, everything.

"Paul Dano was my first choice [for the voice of the space spider Hanus]. I wanted him for his cadence, for his personality. He was perfect.

"But the way you shoot a film like this, there’s no point in recording anything before, so his voice was recorded after the movie was cut. It was a tricky way to make a movie.

"But through it all, what kept on baffling me was this tremendous strength in Adam’s performance, the nature of this thing he’d done.

"I love Adam. He’s the best human being on the planet. He’s a tremendous actor, formidable and amazing. This film would not exist in any shape or form without him."

Carey Mulligan also appears in the film as Jakub's pregnant wife Lenka, and Johan admitted the strength of the two star's performances often left him thinking there was no need to be on set to guide them.

He said: "Carey is the most exquisite actor I’ve ever worked with. She’s so technically perfect and so delightful as a human being. She takes the work so seriously, like I do. I’m a very serious person in what I do. So it was just a joy to work with her.

"I’d say to her once she got into character with Adam, that I didn’t even need to be there on set. I could go home and play with my kids because you guys have got this.

"She’s really a master as an actress, and so versatile. She can do anything. It’s bliss to work with very talented people. It makes my job tremendously easy."