PGuardiola had made the decision. The Manchester City manager had known it for five or ten minutes and when the half-time whistle blew in Wednesday night’s Champions League match against Internazionale at the Etihad Stadium, he sprinted to the dressing room to put his plan into action.

That’s a key part of Guardiola’s greatness. The ability to recognise when and where things are going wrong and make the necessary changes. Not much was going right here. City were blocked, unable to play with more fluidity or incisiveness. They were unusually vulnerable.

Inter radiated confidence – except in front of goal. They built up calmly from the back. They fought their way through City in transition moments. Guardiola was particularly worried when one of his players lost the ball without support around him.

Inter’s deep 5-3-2 formation was both oppressive and strangely captivating. Players rushed from side to side in masses, forcing City to switch quickly, but they were unable to do so. Inter strikers Marcus Thuram and Mehdi Taremi put Rodri under pressure. City’s midfield pacesetter could not unite the action.

Guardiola has faced this challenge before and will do so again – including on Sunday when City host Arsenal as they begin their Premier League title chase. Arsenal left the bus stranded at the Etihad Stadium last season, coming away with a 0-0 draw in March that was clearly on the side of points gained.

Will they adopt a similar approach? That’s easy to assume, especially with their playmaker Martin Ødegaard injured. Mikel Arteta seemed to want his Arsenal side to be difficult to beat at Tottenham on Sunday, with solidity the foundation of the eventual 1-0 win. And if it worked for Spurs after it had worked previously at the Etihad…

There is no doubt that Arteta will be scrutinising every inch of Inter’s performance and drawing ideas from it. Guardiola was asked if the game against Arsenal could be similar and he said he didn’t know; it was up to him to read Arteta’s tactics and react. But he added: “It’s an incredible team again, they defend really well, they don’t give up chances, they don’t concede goals, they’re really good in many aspects, they control everything.” Which, summed up, sounded like a yes.

Guardiola’s reaction to Inter at half-time brought this internal turmoil to light. Kevin De Bruyne suffered an injury in the 44th minute in a collision with Inter goalkeeper Yann Sommer, which makes his participation in the match against Arsenal doubtful.

But Guardiola would have pulled him back anyway, taking Bernardo Silva from the other central attacking midfield position and repositioning him on the right, making room for Savinho. Guardiola wanted his most agile midfielders in that crowded area, and so Phil Foden and Ilkay Gundogan came in. Rico Lewis was ordered to move forward and inside from the right-back.

“Above all, we needed players who could move in tight spaces,” said Guardiola. “Rico, Phil and Gündo are the best we have in that position. In tight spaces. The way Inter defended… I thought about making that substitution for 35, 40 minutes. After what happened to Kevin, the doctor told me he wasn’t ready to play. But I was already thinking about making a substitution at half-time.”

Guardiola hoped to put Foden in a position where he could turn and shoot, or to get Gundogan into the six-yard box. Both scenarios worked, although not with the desired result. Herein lies perhaps the most important lesson from the Arsenal game.

Foden shot straight at Sommer in the 69th minute after being touched by Gündogan in a crowded area; he would have scored from either side. Gündogan missed two headers in stoppage time after converting crosses and the score was 0-0. In games like this, all tactical nuances and maneuvers are narrowed down to a fine point, the gaps vanishingly small. It’s all about being decisive. City must not be blunt on Sunday.

There is one final, related topic of discussion. Rodri has done a lot to bring the issue of player burnout to the forefront. He said that strike action could be an option as the fixture schedule becomes more crowded and the new format adds two extra games in the Champions League group stage.

But Rodri has only started one game this season, as has Gundogan, and Foden has twice come off the bench for 45 minutes. Is City’s engine room ready for such a crucial test? Arsenal will have a near-perfect record from their away games in the calendar year: 11 league games, 10 wins and a single draw. It was the game at the Etihad. City will want to make it different this time.