The 36-year-old fell 7-6 (7-5) 4-6 7-5 to the world number 13, who he has never managed to beat in six meetings.
Murray twice served for the match and missed match point in another gruelling contest lasting just over three hours.
“I’m not really enjoying it just now in terms of how I feel on the court and how I’m playing,” Murray said.
“The last five, six months haven’t been that enjoyable, so I need to try and find some of that enjoyment back because playing a match like that there’s not much positivity there.
“When I play a good point, I’m not really getting behind myself and then in the important moments, that will to win and fight that has always been quite a big, big part of my game,” he added.
Murray smashed his racquet twice during the match against De Minaur and the loss means the Scot has still not won a match at the Paris Masters since winning the tournament in 2016.
Despite his negativity, Murray did not give any indication that he could retire but said he would need to do “a lot of work” if he wants to keep playing.
“It’s not just going to be like one or two weeks of training to get me to where I need to get to, it’s going to have to be a lot of work and consistent work to give myself a chance,” he added.
Murray, who has lost five of his last six matches, failed to convert three match points against De Minaur in Beijing last month and this latest loss in Paris is his fourth against the 24-year-old this year.
His opponent saved set points before pinching a close opening set with a narrow tie-break victory.
Murray recovered with a more assured performance in the second, breaking in the ninth game to level and force a decider.
Murray’s record against De Minaur this year also includes defeats at Monte Carlo and Queen’s, but it looked like the former world number one might break that losing streak after finding himself a double break up in the deciding set.
He had match point at 5-4 but missed it with a long return and smashed his racquet on the floor in anger after handing De Minaur a break-point opportunity, which he took to level at 5-5.
Murray became increasingly exasperated as he knocked the drinks bottles and towel off his bench before failing to hold either of his next two service games and squandering opportunities to force a final set tie-break.
He again smashed his racquet on the floor as he sent a return into the net and De Minaur closed out the win.
