Griffiths has been in outstanding form at Dragons this season, picking up a series of man-of-the-match awards in the Guinness PRO14.
He was not selected for the autumn internationals, however, Marnitz believes he will be next in line for a call-up.
“Ollie has been outstanding since he has come back from injury,” he said. “I honestly think if he bides his time his opportunity will come.
“I would not be surprised if (Warren) Gatland has a shortlist in terms of who is next in and I’m sure Ollie will be very high on that list.
“I think the first casualty of war will see Ollie’s name on the speed dial.”
Marnitz also welcomed the inclusion of Aaron Wainwright as he continues his international development.
“If you asked me a year ago I would say impossible, but Aaron (Wainwright) has been outstanding over the last year.
“It’s no surprise for us. He works tirelessly so we are over the moon for him."
CLICK HERE to secure your tickets for Dragons first home game in the Challenge Cup this season against Northampton Saints on Friday night (kick-off 7.30pm).
