McDermott described the performance as “not great” and stressed: “While it’s great we’ve won, there was too much ugly stuff in the second half for me to say we’ve won so everything’s all right.”
Rhinos’ 20-18 victory over third-placed Hull ended a run of four straight defeats.
The champions climbed above Hull KR to 10th in the table and remain two points ahead of Huddersfield Giants, who pulled off a shock 11-0 victory over Warrington Wolves.
McDermott hailed his side’s “grit and determination”, but said: “Three times this year we’ve played really poorly.
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“Every other time, whether we’ve won or lost we’ve given it a go.
“I don’t think we will come into work on Monday thinking everything’s all right, we are back on the horse.
“That’s not where it’s at. We need to improve and go again. There’s some things we’ve got to get on top of.”
Of his feelings after the game, McDermott said: “I am pleased for a lot of people, pleased for the players and the fans have been great throughout this tough period and you don’t realise how good a club you’ve got until you go through some tough periods.
“The club has been really supportive.”
He added: “There’s some benefits from winning the game and we are really pleased, but at the same time it wasn’t great and we’ve still got some work to do. We’ve been in that mindset win or lose.
“We’ve got some work to do on Monday and that doesn’t change.”
Hull have not won at Leeds since 2007.
They had won their previous five Super League games, but coach Lee Radford said: “Conditions played a huge part in the game, but credit to them for getting the result.
“We have been beaten by the better team – we didn’t take our opportunities.
“It was two depleted sides. They were desperate, we were desperate, but we didn’t have enough in the tank.”