Valencia and new signing Diogo Dalot have both been out of action on the club's tour of the United States, with Darmian selected against AC Milan in the International Champions Cup.
The full-back even wore the captain's armband against his boyhood club in Valencia's absence but Darmian remains determined to leave Old Trafford before the closure of the transfer window.
"I don't think the injury of Antonio is a big injury," Darmian, who is in the final year of his United contract, said.
"I don't know how long he needs to stay out, but at the moment he is the captain, he's first choice.
"I want to play more regularly. Last season, I didn't play much - that's my objective and my ambition.
"That's why I spoke with the manager and also with the club about my future.
"I want to leave but we will see what happens because we don't know."
And former Torino defender Darmian sees a return to his homeland as the most likely destination as he sticks to his guns over a United exit, having been restricted to five Premier League starts in 2017-18.
"It's an option. Yes, probably," Darmian said of a possible Serie A switch.
"We will see what happens. Honestly, I'm waiting. If I stay, I stay and I do what I did up until now. If I go, it is because the offer that another team makes will be good.
"To play for probably the best club in the world is a good thing, and for me, it's an honour to play here and play for Manchester United. But we have to take decisions in our life and this is my decision."