Williams, who faces fellow American Alison Riske in the quarter-finals on Tuesday (July 9) as she looks to win her 24th Grand Slam title, has yet to comment on the fine.
A Wimbledon spokesperson confirmed to Reuters that Williams had been fined, but did not have details of the precise incident – or the date on which it occured.
Fabio Fognini was also fined $3,000 for unsportsmanlike conduct after a rant during his third round defeat to Tennys Sandgren.
The Italian had said he hoped a “bomb” would explode at the All England Club.
Nick Kyrgios was fined $8,000 in total for separate unsportsmanlike incidents in his first and second rounds.
The fiery Australian lost to Rafa Nadal in the second round.
(Production: Francis Maguire)