When the Germany international was introduced as a substitute late in the second half during Bayern's disappointing 1-1 draw at home to Freiburg at the beginning of November, Lisa Muller made her feelings clear.
With the Bavarian side trailing 1-0, as her husband belatedly entered the fray, the frustrated spectator wrote: "More than 70 minutes until he (Kovac) finally has a brain wave."
Mrs Muller subsequently apologised for her outburst.
The Bayern striker is certainly not the only footballer who has had to deal with family members airing grievances in public.
There have been plenty instances of players having their honour defended by those who are closest to them. Goal takes a look at some high profile examples.
Cristiano Ronaldo's sister Katia Aveiro vs UEFA
Five-time Ballon d'Or winner Cristiano Ronaldo has his fair share of detractors, but he can always count on his sister, Katia Aveiro, to leap to his defence.
Back in August, she was quick to air her discontent when her brother lost out to Luka Modric for the UEFA Player of the Season award, posting a graphic comparing the two players' stats in the Champions League.
"OK!!!" she wrote on Instagram when Modric scooped the accolade. "Everyone can draw their own conclusion."
Ronaldo's agent Jorge Mendes echoed Aveiro's sentiment and went one further by describing the snub as "shameful".
A month later, Aveiro responded to Ronaldo's red card against Valencia in the Champions League with similar levels of indignation, suggesting that an elusive 'they' want to "destroy" her brother.
"Football's shame... justice will be served," Aveiro blasted on her Instagram account.
"They want to destroy my brother but God never rests. Shameful."
Gonzalo Higuain's brother Nicola vs Napoli
In April 2017, Gonzalo Higuain's brother Nicola - who is also the player's agent - took to Twitter to indulge in some old-fashioned gloating at the expense of Napoli president Aurelio De Laurentiis.
Higuain scored twice at the San Paolo for Juventus in a Coppa Italia bout between the sides and, though the Bianconeri ultimately lost the game 3-2, Nicola could not resist having a dig at the Partenopei chief.
Come mi piace vedere la faccia di Aurelio ogni volta che segna mio frate. ⚽️⚽️👌. Alla prossima pres. Hahaha!!!.— nicola higuain (@NicolaHiguain) April 5, 2017
"How I like to see Aurelio's face when my brother scores," he tweeted with glee. "See you next time Mr President. Hahaha!!!"
Clearly, Nicola has his priorities straight when it comes to his client-brother...
David de Gea's girlfriend Edurne Garcia vs Manchester
At the time, the Spain international was heavily linked with a move away from Old Trafford and his girlfriend, singer Edurne Garcia, stoked the flames when she agreed with the summation that Manchester was "uglier than the back of a fridge."
"I've been told Manchester is uglier than the back of a fridge," Pablo Motos, host of entertainment show El Hormiguero, put to her in an interview.
Garcia agreed with Motos and added: "It's not very nice, that's for sure. You have to hunt out specific places - the nice places.
"But even then Spain is nicer. The reason I like it is because David's there. With him being there, everything is wonderful."
Luckily for Manchester United fans, Garcia's dim view of the city doesn't seem to have impacted De Gea's position at the club - three years later he remains a key figure and excelled in the subsequent seasons.
Claudio Marchisio's wife Roberta Sinopli vs Juventus
Italy international Claudio Marchisio certainly knows his wife, Roberta Sinopli, has his back because she never shies away from showing her support for her husband online.
The end of Marchisio's Juventus career was blighted by injuries and his time on the pitch diminished severely as a result.
In February, it became clear that the midfielder's lack of match action was beginning to grate as Sinopli shared a pointed post on Instagram declaring that "tolerance has a limit".
Marchisio eventually departed Juve a few months later in order to join Russian outfit Zenit and Sinopli made her feelings on the matter known as she responded to a Tuttosport tribute to her husband.
"In life, as in cinema, it is better to be a regret than to be endured," was the line she stressed.
Andrey Arshavin's wife Yuliya vs England
Former Arsenal star Andrey Arshavin suffered a similar issue to De Gea when he first arrived in North London from Zenit in 2009.
The ex Russia international's ex-wife Yuliya Baranovskaya expressed a keen disdain for "boring" England and its "disgusting" cuisine, suggesting that the only redeemable feature was the fact that Victoria Beckham was a resident.
She wasn't alone in her struggle to adapt to British culture though, as Arshavin experienced the same annoyance.
He spent four years at Arsenal before the homesickness became too much and he returned to Zenit
Samir Nasri's girlfriend Anara Atanes vs Didier Deschamps
Anara Atanes fired shots at Les Bleus coach Didier Deschamps in a series of expletive-laden tweets.
"F*** France and f*** Deschamps. What a s*** manager," wrote Atanes.
She quickly followed that up with another tweet: "In case you didn't read my tweet properly.... I'll repeat myself...f*** FRANCE!!!!! And f*** Deschamps!
"Let's just get this straight. I'm not mad I get my boyfriend for two months. I just think there's a level of respect to be had #shouldhavebeenspanish."
Nasri responded to Atanes' angry rant with a more mature, zen-like message: "Love you dont get upset, life sometimes is unfair but you have to accept it and deal with it."
Adrien Rabiot's mother Veronique vs PSG
His mother, Veronique, has been a vocal proponent of her son in the media and has butted heads with PSG in the past, even handing in a transfer request on the player's behalf.
"If I speak today, it is to restore the truth. I do not want supporters to have a false image of Adrien," she said.
"I find an interview unveiled and transformed in the press... And I ask the question, where does this distorted version come from?
"Does it suit the club to get off Adrien because we asked for a transfer?"