Di Maria hopes the Copa del Rey can spark his side back to life.
"I think we can do it. We know it's very difficult to win the league, and the cup and Champions League are two major objectives left this year. And that's an important motivation.
"We need to be at the same level as we played against Celta," he added, referring to their success in the previous round when they won 4-0 in the second leg after trailing 2-1 from the first.