Williams was given a code violation, a penalty point and a game penalty for the outburst which occurred during her loss to Naomi Osaka at the USTA Billie Jean King National Tennis Center in New York City and Federer suggested in an interview with The Sunday Times that Williams should have handled herself in a more professional manner.
"It's a melange of all things, but at some point, I feel like Serena should have walked away", Federer told The Times.
"Of course I'm happy that I won a Grand Slam, I don't think there's anything that can take away from that, but I feel like it was so odd, I didn't just want to think about it".
'She did (walk away) but she went too far. "She should have walked earlier".
Federer, though, did suggest the actions of the 23-time Grand Slam champion had been "a little bit excusable".
'The umpire should maybe not have pushed her there. "It's unfortunate, but an incredible case study".
Williams's outburst in the second set of the US Open final overshadowed Naomi Osaka's 6-2, 6-4 victory, in what was the 20-year-old's maiden appearance in a Grand Slam final.
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Williams told Ramos that she would "never cheat to win", though Mouratoglou did later admit that he had been coaching from the box.
Williams, 37, was given a first code violation after umpire Carlos Ramos judged a gesture from coach Patrick Mouratoglou to be coaching.
When the game finished, she called him "a liar" and "a thief".
Osaka eventually admitted her US Open victory had been a "bittersweet moment". The incident led to a $17,000 fine from the United States Tennis Association.
Federer has been in stuttering form since clinching his 20th Grand Slam title at the Australian Open at the beginning of the year.
She wore the outfit at the tournament in May, and said it made her "feel like a superhero".
"Serena has worn crazier stuff in the past". For me, it was a bit of nonsense.
"I was totally on the women's side". The views expressed therein are not necessarily those of stlucianewsonline.com, its sponsors or advertisers.