Germany begins its final preparations for the upcoming tournament with a send-off in Mainz against Finland, before facing United States on 7 June (AEST).

Neuer was a surprise inclusion in Nagelsmann's squad, having retired from international football after UEFA Euro 2024. But after insisting he would not return, he made a U-turn to be involved.

The 40-year-old is going to be Germany's No.1 at the FIFA World Cup, but having suffered a minor calf injury, his preparation is being interrupted.

But Nagelsmann says he is still on course to feature in their opener against Curacao on 15 June (AEST), with his recovery on track.

"He's been running, it's looking good," Nagelsmann said of Neuer. "He has no problem, and all is going to plan.

"We'll make a decision before the USA friendly."

While Neuer is not set to be involved against Finland, Nagelsmann already has three set starters in mind, with Bayern Munich youngster Lennart Karl among those to be named in the team.

"Lennart Karl will start," Nagelsmann added. "He made a very good impression in training.

"But we have different options and profiles in Jamie [Leweling] and Leroy [Sane]. Lenny will get his chance to show what he can do.

"Felix Nmecha and Aleks Pavlovic will start in midfield. As of [Saturday], Deniz Undav will start upfront."

Neuer is set to surpass Lothar Matthaus as Germany's oldest player.

Should Germany reach the final, and Neuer play in every match, then Neuer will move above Lukas Podolski (130) and Thomas Muller (131) into third place for the most caps for Germany, trailing only Miroslav Klose (137) and Matthaus (150).

Germany will make its 21st FIFA World Cup appearance this year, more than any other European nation and second only to Brazil (23) overall.

Since missing the tournament in 1950, Germany has advanced beyond the first round on 16 of the past 18 occasions, but failed to reach the knockout stages in both 2018 and 2022.

It did, however, make it through to the semi-finals of UEFA Euro 2024 before being eliminated by eventual winner Spain, and Jamal Musiala believes the unity in the team can help it go on a similar run at the FIFA World Cup.

"The team has gelled a bit better since the Euros; the automatisms are very similar, sometimes even identical," Musiala said.

"Now we notice that when we repeat things, it doesn't take as long for them to work well as before. Now it's very harmonious, everyone gets along well."