Aymeric Laporte has played exactly 200 minutes since returning from a serious knee injury and Manchester City have not conceded a goal in that time.
The Premier League champions have at times this season been an imitation of the team that dominated English football for much of the last two years, since the French defender damaged his cartilage and lateral meniscus in August. With him back, City are again getting close to their best.
His presence alone transmits reassurance and a meanness through the back five and gives City a platform for their attacking domination. It's why they will travel to Real Madrid with a little more confidence than they would have done only a few weeks ago.
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Conceding too many goals has been the biggest reason for City's failure in Europe, particularly under Pep Guardiola. Under a coach that won the Champions League trophy twice with Barcelona, they were knocked out when Monaco scored six over two legs, Liverpool five and Tottenham four.
To claim that first ever Champions League success that they crave, they must curb their generosity. They have already conceded more Premier League goals this season than in their previous two. And they have kept just three clean sheets in their six Premier League game since the turn of the year; Laporte started all of them.
Laporte hasn't, however, played a full match yet but Guardiola insists he can play the whole 90 minutes at Santiago Bernabeu. He came off in the 57th minute of the 1-0 victory over Leicester on Saturday and the City boss says he is still getting up to full fitness after two appearances in four days.
"He asked me to be substituted, but he's not injured," Guardiola said. "He's been four months, five months injured, we can't forget that. He had to run a lot. It was different against West Ham, we could control it easier. He's okay."
City will hope the coach's diagnosis is correct following the early substitution because Laporte's presence in Madrid on Wednesday night could be critical.
Ironically, two rare Laporte errors in last season's quarter-final second-leg defeat to Tottenham proved costly, but they were more an aberration than a precedent. Against Leicester there were some signs of rustiness but it was another big step forward ahead of the last-16 game in Spain after the half-paced training session against West Ham last Wednesday.
The Foxes, pushing to try to overtake City as the next best to runaway leaders Liverpool, were a real test for the defence and Laporte's role as its linchpin.
He was caught dawdling on the ball in the seventh minute and it led to Leicester's best chance with Jamie Vardy running through on goal and slamming a shot against the foot of the post.
The England striker has proved in recent seasons that he is the biggest threat to City's tactic of defending with a high line, with his pace to run onto balls over the top always a problem. He scored at the Etihad Stadium just before Christmas, but did not in Saturday's rematch.
Anyone trying to second guess a Guardiola line-up can often look foolish but it would be expected to see Laporte start alongside Fernandinho at the heart of the defence against Madrid.
The pair were starting together for the second time and it was a valuable outing as a partnership, Laporte covering his Brazilian team-mate when he was occasionally out-paced by Vardy.
Real will offer an entirely different threat and Guardiola said ahead of the game that there would not be too much to learn in preparation for the trip to Spain other than the opportunity to gain momentum.
But there were some lessons for his players. Twice they gave away dangerous free-kicks on the edge of the box with clumsy challenges - one forcing a save from Ederson and the other hitting Kevin De Bruyne on the arm, which Leicester boss Brendan Rodgers thought should have been a penalty.
But spot-kicks is the biggest challenge they have ahead of Madrid. Sergio Aguero's poor penalty was saved by Kasper Schmeichel and City have now missed five of their last seven chances from the spot.
"It's not normal for the quality we have, but like I said to them the next one we're going to score and the taker must be convinced, practice and be convinced and do it," Guardiola said. "We didn't score against Spurs in the Champions League last season, this season against Spurs we missed a penalty - in this kind of games it's a big difference.
"I like the mentality, I like Sergio taking the ball and wanting to take it. Practice, be positive, one idea, shoot and score a goal."
Laporte will be key to shutting down opponents but they can't afford to miss such big chances at the other end.
