Mikel Merino says he is seeing football in a different way after his first month or so under Mikel Arteta at Arsenal. The Spain midfielder made a belated debut in Tuesday’s 2-0 Champions League home win over Paris Saint-Germain, having recovered from the shoulder blade fracture sustained in his first training session.

It has been a frustrating time for Merino, who signed from Real Sociedad for £31.6m at the end of August, and there was delight and relief for him when he came on as a 64th-minute substitute, taking his place alongside Declan Rice. His initial impression of his new club, specifically the intensity and meticulousness of the training, echoes how Rice felt after he joined from West Ham in the summer of last year.

Related: ‘This is the year’: Bukayo Saka backs Arsenal to win Premier League title

Rice said he thought he knew about the game but “when you meet managers like Mikel [Arteta], you realise you don’t really know anything”. Merino has been similarly blown away even though he has spent most of his time on the outside of the sessions. The injury misfortune has perhaps offered him a different perspective.

“It’s something that is amazing” he said. “They do some things that I have never seen in my career. The methods they use are completely new to me so it takes some time to adapt. But at the same time, when you get it you are in a different level because they challenge you every single day – not only physically but mentally. It makes you be sharp mentally and that’s what you are going to find out in the game.

“I don’t want to tell everything that we do but there is no rest between one moment and the other. They are always challenging you mentally with different stimuluses. It makes you all the time aware of what is happening around you.”

Merino arrived at Arsenal as a Euro 2024 champion; his big moment was the 119th-minute headed winner against Germany in the quarter-final. But he was stopped abruptly in his tracks after a freak collision with Gabriel Magalhães. According to Arteta, Merino landed on the ground and Gabriel fell on top of him.

“It was such an unlucky moment,” Merino said. “I haven’t seen an injury like this. It was not the best timing but I like to look at the pros, the bright side of it. This gave me a lot of time to think, to get to know my teammates, to get to know the staff, to work on myself – the things that I need to do in terms of tactics, in terms of physicality, and I think I am a much better player now than I was four weeks ago.

“It was really tough mentally. To come in here, you want to have a nice few days to show everybody what you are capable of, to show why they have put faith in you and then the first thing that happens is you break your scapula. But everybody in the club was really nice to me, really lovely, and finally I can say I am officially an Arsenal player now. I have made my debut and I am buzzing.”

Merino’s English is excellent, a legacy of his season at Newcastle in 2017-18. That did not work out how he wanted, his playing time limited, but it helped to hone a fighting instinct that was a part of the attraction for Arsenal. Merino has a streak in him, as football people like to say, and at 6ft 2in he is imposing. “I am who I am because of the Premier League: it made me harder, stronger, taught me to take the hits,” he told the Guardian in 2021.

It will be interesting to see how Arteta uses Merino, who played as more of a No 8 for Real Sociedad, with Martín Zubimendi the No 6. Arsenal tried to sign Zubimendi last year, as did Liverpool this summer. Arteta has come to see Rice as a No 8, which is where the England caretaker manager, Lee Carsley, played him during the September internationals against Republic of Ireland and Finland.

In the absence of the injured Martin Ødegaard, Arteta has set up with two central midfielders behind a pair of mobile central attackers – Kai Havertz and Leandro Trossard. It has been a box formation. It could be that Merino and Rice can dovetail, taking it in turns to hold or push up. The roles may not be fixed.

“I want to grow, I want to learn even more,” Merino said. “When I spoke to Mikel and I saw what was the plan … not only with me but the whole team, what was the culture … I felt this was the right place to take the next step in my career.

“The mentality they have here is amazing, not only on the pitch but at the training ground – how they focus on the single things, the details, the basics. Winning trophies is the main thing for everybody. They are obsessed with that.”