Arsène Wenger expects this Premier League season to be the hardest he has encountered during his time in charge of Arsenal, saying the “spectacular” spending of rivals such as Manchester City makes the task of winning the title more challenging than ever.

Arsenal begin Wenger’s 21st full campaign in north London with a home match against Leicester City on Friday evening, and a fast start is considered vital after their failure to qualify for the Champions League last term. Manchester City have led the division’s summer spending with a £217m outlay on new signings; Wenger believes as many as seven teams could be involved in the title race but notes that Arsenal’s opponents, particularly Chelsea and Tottenham Hotspur, are not without problems.

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Asked whether this would be his most difficult season, Wenger said: “Yes, because look at what City have done. They have been quite spectacular in the transfer market, Manchester United as well. And it’s not finished – Chelsea have bought [Álvaro] Morata and have not lost [Diego] Costa yet, and they will certainly buy more. In the middle of the transfer market it’s difficult to predict. At the moment the most active have been United, City and Liverpool a bit.”

Wenger said Arsenal, who continue to be linked with the Nice midfielder Jean-Michaël Seri, are “still open” to making further signings, with Sead Kolasinac and Alexandre Lacazette their two first-team arrivals this summer. “At the moment I have 33 players and it’s very difficult to manage such a high number on a daily basis,” he added, hinting that squad players – almost certain to include Lucas Pérez, Kieran Gibbs and Calum Chambers – will have to be moved on before further incoming movement occurs.

At first glance it appears his opposite number at Chelsea, Antonio Conte, would envy that situation. The squad lists shown before last Sunday’s Community Shield at Wembley showed 17 more players available to Arsenal than their opponents, and Conte’s frustration at a lack of additions is widely known. Chelsea have, though, sent 18 players out on loan in pre-season and Wenger suggested they have contributed to the slimness of their own resources.

“Maybe yes, he has the opposite problem,” Wenger said of Conte. “But if you look at the number of players that are out on loan, they can call a few back. I have sympathy for him but do I feel sorry for Chelsea because they don’t have enough players? Then no.”

Tottenham Hotspur are another contending team experiencing flux, primarily through their temporary move to Wembley. They lost to Monaco and Bayer Leverkusen at the national stadium in last season’s Champions League; Wenger said any problems they faced would largely be psychological but queried whether they will play in front of full houses and the effect failing to do so might have on Mauricio Pochettino’s team.

“I think it is all a little bit in your head,” he said. “For a while you had the problem of the quality of the pitch but that does not exist any more. Today the pitch is of a similar quality to everywhere. After that, the difficulty is to fill it, nothing more. In England we are not used to playing with half a stadium empty. So can they fill it in every game? I don’t know. A full Wembley Stadium is fantastic.”

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After the win over Chelsea last weekend Wenger suggested eight teams can win the league but speaking before the Leicester game, he revised that figure slightly and showed his working. “Maybe I was a bit positive,” he said. “I took into account the four who finished in front of us [last season]. Then if you include us and Manchester United, and there could be a surprise like Leicester. [Or] teams like Everton. You can have seven.”

Wenger stated his belief that qualification for the Champions League should be decided purely by league position rather than success in the Europa League – in which Arsenal will play this season – but said he had been overruled by most of his peers at Uefa-led meetings in Geneva. “I was always, honestly, not for it,” he said. “But we will focus first on the Premier League; for us it is the most important.”

Arsenal have a number of fitness concerns before Leicester’s visit. Alexis Sánchez has already been ruled out with an abdominal problem, while there are doubts over Mesut Özil, Aaron Ramsey, Per Mertesacker and Shkodran Mustafi. Laurent Koscielny serves the second of match of a three-game ban.