LENS, France — Per Mertesacker believes the big spending by Arsenal’s main rivals will make it harder for the Gunners to challenge for the Premier League.

Mertesacker has taken note of the big signings arriving at Manchester United, Manchester City and Chelsea and said it’s clear they will all be stronger than last season, when the traditional powers struggled.

“That’s what I expect, so we need to be stronger as well,” Mertesacker told reporters in Lens after Arsenal’s first preseason game. “We [will] try to get fit and compete for the title, but on the other hand there will be some other teams who are really looking forward to this season with a lot of new players.”

Arsenal’s only major signing so far has been Granit Xhaka, with Arsene Wenger’s search for a new striker yet to bear fruit. In comparison, United and new manager Jose Mourinho have added Zlatan Ibrahimovic and Henrikh Mkhitaryan to their attack, and are reportedly close to a world-record transfer deal for Paul Pogba.

Chelsea, meanwhile, have spent more than £60 million on N’Golo Kante and Michy Batshuayi.

“[There have not been] a lot of signings [for Arsenal], just one, two or three signings and a lot of young players as well. So that’s the way it is at the minute,” Mertesacker said. “It won’t be easy this season, especially with all the signings going [at other clubs]. A lot of business is already done.”

But the German also cautioned that adding too many new players could backfire for clubs if they don’t gel together quickly.

“It needs to fit,” he said. “You cannot predict what is going on with the other teams, even when you have three, four big signings you need to complement each other. There are a lot of questions, I think.”

Arsenal have a tough start to the season as they face Liverpool and champions Leicester in their first two games, and they could still be without a handful of their top players who will just be returning from holiday after international duty.

But Mertesacker said that could provide a chance for some of the younger players to make an impact.

“We have a couple of young guys and it’s a showcase for them now really. And they can really show what they are capable of,” he said. “Arsenal was always open to young players, especially Arsene, for them to develop if they have a promising start. So there is a good chance now. We have got a lot of players missing, and there are lot of pieces missing from that puzzle. We will hopefully have a good fit at the end when we start.”

And even if Arsenal were to falter in their opening games — potentially leading to a repeat of the fan anger of last season — Mertesacker is convinced the Gunners can bounce back from any negativity.

“I think we are always able to put all the negative energy away from us,” he said. “That was always our strength throughout the last five or six seasons. When all the negative energy came we bounced back straight away. So we are used to it. I’m not going to say we use it always as motivation … [but] no matter what happens we always find an answer.”

Arsenal have been linked with Mauro Icardi, Gonzalo Higuain, Alexandre Lacazette and Riyad Mahrez and have been publicly rebuffed by Jamie Vardy but Arsene Wenger remains confident he can improve his squad.

“It’s not over. Today we are in July, and the transfer market finishes on the 31st August,” Wenger said following the 1-1 preseason draw with Lens. “We know as well that a lot happens many times in the last week. It’s a long time to go, but we are active. We are working.”