Loew had a contract until the Euro 2020 finals, but Grindel had previously stated his job is safe regardless of how Germany perform at the 2018 World Cup finals, which kick-off next month.
The preliminary squad must be whittled down to just 23 players by June 4.
"We've been in constant contact with Manuel".
The 30-year-old Wagner has scored four goals in his eight internationals and was part of last year's Confederations Cup-winning team. "What is clear is that without match practice to go into a World Cup is not possible".
Low has until June 4 to submit his final 23-man squad that will represent Germany in Russian Federation and attempt to become the first back-to-back World Cup winners since Brazil in 1962. He wasn't able to show his incredible quality.
Midfielders: Julian Brandt (Bayer Leverkusen), Julian Draxler (Paris Saint-Germain), Leon Goretzka (Schalke), Ilkay Gundogan (Manchester City), Sami Khedira (Juventus), Toni Kroos (Real Madrid), Mesut Oezil (Arsenal), Sebastian Rudy (Bayern Munich).