The Rhinos suffered only their third defeat of the Super League campaign as they went down 6-24 at the Halliwell Jones Stadium.
"We were well beat," McDermott is quoted as saying by Sky Sports News. "It was not good. We've got a few things we need to address there.
"They beat us off the ground. They played a bit too quick for us off those early exchanges. They played a bit too tough for us. They played a bit too fast for us."
Leeds return to action on June 6 when they host Leigh Centurions in the quarter-finals of the Challenge Cup.