According to Ruhr Nachrichten, the 21-year-old centre-back has been one of the standout performers of Borussia Dortmund's pre-season, climbing above his compatriot and positional rival in the club's internal rankings after a summer of visible improvement.
Head coach Niko Kovac credited Mane's application for the turnaround.
"Filippo is making progress. That's down to his hard work. We've adjusted things, we know which problems he had. We've improved that over the past weeks and months. If he stays consistent with his fitness, he'll certainly be a good player for us," Kovac said.
The shift has real consequences for Reggiani, who made eight appearances for Dortmund's first team last season despite his own development being disrupted by injury.
According to WAZ, the teenager currently has two options on the table: regular football with Dortmund's second team, or a loan move away from the club before the transfer window closes. Sporting director Lars Ricken indicated the club is in no rush to force a decision on the matter.
"There's no pressure on that front. We'll assess the situation case by case as the transfer window gets closer to closing," Ricken said, referring to the possibility of a loan for younger players in Reggiani's position.
Reggiani's progress has not gone unnoticed back in Italy, despite the setback to his standing at Dortmund. He earned his senior debut for the Italian national team in June, and Serie A clubs are reported to have expressed interest in working with him, giving him options beyond Germany should Dortmund ultimately sanction a temporary exit.
For now, the pecking order at centre-back has swung firmly in Mane's favour heading into the new Bundesliga season, with Kovac's public endorsement suggesting the 21-year-old is set for a more prominent role than he held last term.
The reversal is a striking turnaround from earlier this year, when Reggiani had been the one to seize his chance after an injury to Mane opened the door to regular first-team minutes and helped him establish himself as a fixture in Dortmund's defence during the second half of last season.