"There is no love interest," said the 40-year-old Transformers star. "It's a great supporting part."
Josh appears opposite Maria Bello and Laura Dern in the film, playing a counselor to a drug-addled DJ (played by Lucas Till).
"It was really awesome that somebody believed I could play a counselor. I said 'Really! You think me? I shouldn't be counseling anybody,'" he joked before adding, "It's nice to be able to do things outside of what people [normally] see you as."
As much as he's enjoying this current part, Josh will be putting his career on the back burner for a bit as he approaches the arrival of his son with wife Fergie.
"I plan on taking as much time as I can off just before and as much time as possible after," he told ET Canada. "I can't imagine having a kid and then not being able to be there, that would just drive me crazy."
Watch the video for more. Strings opens May 2, 2014.