Peretz landed in Munich earlier on Friday but Tuchel said the deal was not yet done.
"We are trying very hard for him to become our player," Tuchel told a press conference. "Hopefully he will soon be in our squad. The medical and some signatures I think (remain) but there can always be surprises."
Bayern had scouted the keeper weeks ago as they looked to bring him in for the first part of the season, with Germany international Neuer still weeks away from a comeback after suffering a broken leg in December.
Bayern opened their Bundesliga season with an emphatic 4-0 victory at Werder Bremen last week with Bundesliga record signing Harry Kane scoring one goal and setting up another on his league debut.
That win came less than a week after their surprise 3-0 home loss to RB Leipzig in the German Super Cup.
Veteran Sven Ulreich was in goal for Bayern in both matches, with Yann Sommer and Alexander Nuebel having left in the close season.
Against Augsburg in the Bundesliga on Sunday, Tuchel will be without midfielder Jamal Musiala, who picked up a hamstring injury in training this week and will be out for an unspecified period of time.
Asked whether that meant that crowd favourite Thomas Muller, who was a substitute against Werder, would start, Tuchel said: "It could be Muller but it could also be Serge (Gnabry) or Ryan Gravenberch. You will have to wait and see."
"He (Muller) could start but I don't think he is at the level to play through." Mueller missed much of the pre-season preparation with an injury.
"So the decision will be whether he plays at the start or the end," Tuchel said.
