Roger Federer was knocked out in the semi-finals of the season-ending event in London.
Alexander Zverev saw him off before beating Novak Djokovic in the final to win the biggest title of his career.
But Mirka was in no mood to share her man after one fan asked if she was up for swapping husbands.
Caught on camera by Tennis TV a fan holds up a banner that reads “Hey Mirka, wanna swap?”
But the camera then pans to Mrs Federer who shakes her head before taking a sip from a bottle.
Federer is set for some time off after another gruelling season comes to an end.
He will spend some time in Dubai recovering before next season, which he will kick off in Australia with the Hopman Cup in Perth and then the Australian Open.
Federer, 37, finished this year ranked No 3 in the world behind Rafael Nadal and Djokovic in No 1.
He won four titles in 2018 including the Australian Open, with success in Basel, Stuttgart and Rotterdam.
It comes after a stunning 2017 saw him win two Grand Slams and seven titles in all.
“I must tell you I’m very proud that at 37 I’m still so competitive and so happy playing tennis,” he said after losing to Zverev in the ATP Finals semi-final.
“From that standpoint, as disappointed as I might be about this match, if I take a step back, I’m actually very happy about the season.
“It’s been a historic season in some ways. Got back to World No. 1.
“For me, that was a huge moment in my life, to be honest, in my career because I never thought I would get there again.
“[Pete] Sampras once upon a time said, ‘If you win a Slam, it’s a good season’.
“So [my season] started great. I played super well in Australia again. So obviously I can’t wait to go back there in a couple of months.
“The second half of the season could have been better, maybe. I also have high hopes to always do well.
“So I’m happy I gave myself opportunities again in that second half of the season. I maybe lost a couple of too-close matches that could have changed things around for me a little bit.”