Mauricio Pochettino explained he simply could not risk Neymar as he is "not in a condition to compete" against former club Barcelona on Wednesday.
The world's most expensive footballer suffered an adductor injury playing for Paris Saint-Germain against Caen in the Coupe de France on February 10.
Initial predictions suggested Neymar could return for the Champions League last-16 second leg this week.
PSG won the first match 4-1 at Camp Nou and Neymar has been progressing in training, with Pochettino repeatedly insisting he was on schedule.
But the head coach acknowledged last week he was not guaranteed to be back in the squad for the visit of the Blaugrana.
A medical update from the club on Tuesday subsequently confirmed Neymar would miss out, and Pochettino added in his news conference that an appearance had become unrealistic.
"It is not a decision," he told a news conference. "The fact is the player cannot play. He is not in a condition to compete.
"He made a great effort to get back quickly, but the goal is not just the Champions League.
"It's a difficult time for him but I hope he can come back as soon as possible."
Wednesday's encounter will be the 21st game Neymar has missed this season, playing just 18 times in all competitions.
Since joining PSG in 2017, he has made 25 Champions League appearances - scoring 20 goals and assisting nine - but only six of these outings have come in the knockout stages. Five of the six were in the 2019-20 run to the final.
Although Neymar will be absent again, he at least will not be in the opposition XI as he was just months before moving to Paris, inspiring Barca's epic 6-1 second-leg win to complete a remarkable aggregate comeback in 2016-17.
However, Barca were at home for the second leg on that occasion and no team in the history of the European Cup has advanced after reaching the halfway point of a tie three or more goals behind with the away match still to play.
Pochettino, only appointed at PSG this year, certainly has no concerns about history repeating itself, even if he is guarded against complacency.
"For us, the past goes back to January 3, when we joined the club," he said.
"It's a game we have to go through to reach the next round. That will be our approach from the first minute.
"We have to be consistent for 90 minutes. In football, the most important thing is to be focused.
"We're going to start as if it were 0-0 and we want to win to qualify."
That focus means Pochettino had little interest in entertaining talk on the future of Kylian Mbappe, the hat-trick hero in the first leg.
"This is a situation that the club has been managing for a long time," Pochettino said. "As I have always said, both sides must agree.
"But both the club and the player are focused on meeting the goals that the club set at the start of the season, arriving at the end of the season having achieved or gone close to those goals."