Bild reported Hummels is considering a departure after starting only three times in the Bundesliga this term (h/t Mirror's Aaron Flanagan).
Jerome Boateng and Niklas Sule have been Kovac's preferred central-defensive partnership, while Javi Martinez is another option—the Spaniard has two league starts to his name this season.
Bleacher Report's Alex McGovern attested to Bayern's strength in depth in the position, which suggests they would maintain a quality contingent of centre-backs even if Hummels leaves:
Alex McGovern @AlexMcGovern11
There's a bunch of clubs with stupidly good CB corps: Juve: Chiellini, Bonucci, Benatia, Barzagli, Rugani Bayern: Boateng, Hummels, Sule, J.Martinez Inter: Skriniar, De Vrij, Miranda, Ranocchia Spurs: Vertonghen, Alderweireld, Sanchez, Dier Real: Ramos, Varane, Nacho,Vallejo
It's no secret that the Red Devils are in the market for a new defender despite the arrivals of Eric Bailly and Victor Lindelof, both 24, in recent years.
Hummels is a more recognised, world-class force in the role and illustrated his leadership qualities with the opening strike in his side's UEFA Champions League draw against Ajax (U.S. only):
His age could be a deciding factor in whether United make a move, however. The club vetoed a move for the 29-year-old Tottenham Hotspur defender Toby Alderweireld in the summer because they felt the signing was too shortsighted, per Samuel Luckhurst of the Manchester Evening News.
Bayern's stalwart is four months older than the Spurs centre-back and, by that same logic, would be an even shorter-term fix—Hummels turns 30 in December.
It was reported in the summer that Bayern had won the race to sign Stuttgart defender Benjamin Pavard, a potential heir to Hummels, though the player denied those claims in an interview with L'Equipe (h/t Goal's Sacha Pisani).
Jose Mourinho's certainly wouldn't leave the German out of his team, though it's debatable whether the 2014 FIFA World Cup winner would trade Bayern for the Old Trafford club in its current messy state.