Four and a half months, 138 days, nine La Liga games. One defeat at Camp Nou on Sunday and that might well be that.
If Florentino Perez's mind is already made up, the result against Barcelona may not matter. A draw, or even a Madrid win, is not beyond the realm of possibility. After all, this game rarely has much respect for form and Lionel Messi is injured.
"It's a great game for us in this moment because we have no choice but to stand up, we have to show how good we are against a difficult opponent and I think we can do it," Toni Kroos told AFP this week.
A surprise success would make sacking Lopetegui harder to justify but five games without a win, more than eight hours without a goal, these are not quickly forgotten either.
There were disgruntled whistles at full-time on Tuesday, the home fans deflated after watching a team that featured UEFA's best goalkeeper, defender and player hang on for a 2-1 victory over Viktoria Plzen.
After the match, Lopetegui talked about turning points and changing dynamics but his demeanour perhaps betrayed the truth. "I don't often smile anyway," he said. Madrid's chaotic performance had weakened his position, not strengthened it.
Real loss adds zing to Madrid derby
Isco insisted on Monday that if they fire the coach, they should fire the players too. Lopetegui might have added the one the club did let go last summer took an average of 50 goals a season with him.
Players though are never accountable - certainly not ones crowned European champions only five months ago - and besides, the coach sets the tone.
He instills confidence, which leads to creativity and precision. He also sets the rules and for some, perhaps Perez included, this team has been indulged for too long.
For their part, the players might argue they have struggled before and come through, not least under Zinedine Zidane last season.
"The confidence, in my opinion, is not a problem," said Kroos, whose Germany coach Joachim Loew is among those considered a potential successor to Lopetegui.
"We have many champions in the World Cup and the Champions League, and we have shown we can turn around tough situations. Remember that in the last few years, we have not only played good games, there have been bad ones too.”
He added: "We are creating, we are doing everything we can to get good results and that proves we are behind the coach. He is a very good coach in my opinion and I'm confident we can turn this around with him."
Opposite Lopetegui this weekend will be Ernesto Valverde, watching his Barca side with their own superstar extracted too.
This will be the first Clasico without Lionel Messi or Cristiano Ronaldo since December 2007. The strikers then included Ruud van Nistelrooy and Robinho for Madrid, Samuel Eto'o and Ronaldinho for Barcelona.
Messi will return, in three weeks if his right arm heals as expected, but Ronaldo's permanent absence has weighed heavier with every chance missed.
Barca look to reclaim Champions League title
When Barca went three games without a win last month, the feeling was both clubs were in crisis. Lopetegui was under pressure, but so was Valverde.
Then Messi blew away Tottenham at Wembley and, a day later, Madrid lost 1-0 to CSKA Moscow, lacking the snap and spark Ronaldo once provided and that Messi had given the night before.
Momentum has diverged since. Two more Madrid defeats followed to leave Lopetegui on the brink while Barca are now 10 points from 12 and top of the table.
"Madrid will be even more dangerous, they will come here to demonstrate all the strength they have," Valverde said on Wednesday.
He also knows failure to put away a wobbling rival will see the doubts circling again, but win, and a seven-point gap opens up.
Or, Madrid can cut it to one, with only a single game, at home to Real Valladolid, against an opponent in the top half before Christmas. It will either be a chance for a Lopetegui revival or, the perfect start for his successor.
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