"If he travels with us, he'll be no.1," said Löw in an interview with German broadcaster Sportschau on Saturday. This came after comments to publication Sportbild, in which Löw said he was "optimistic" regarding Neuer's participation at the tournament. "He'll go either as fully fit or not at all. It won't be that he goes with us as a captain who just sits on the bench," added the 58-year-old.
Neuer, who has joined up with his Germany teammates at their training camp in Südtirol, completed two full weeks of training with Bayern before being named on the bench for last weekend's DFB Cup final defeat to Eintracht Frankfurt.
Bayern's number one has not played competitively since suffering a second metatarsal break in the space of six months in a Bundesliga game against Mainz on 16 September 2017.
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Although time is fast running out for Neuer to prove his form and fitness for this summer's showpiece in Russia, he could target Germany's 2 June friendly against Austria as the chance to show that he is ready to play his part in the world champions' title defence.
Should he make the final 23-man squad - which is set to be announced on 3 June - he would almost certainly be given a run-out in the 8 June friendly against Saudi Arabia.
Germany begin their World Cup campaign against Mexico in Moscow on 17 June. Sweden and South Korea complete Group F.