The 2014 No. 2 overall draft pick out of Duke missed all but 25 games as a rookie in 2014-15 due to the same injury.
As seen in the following video, Wednesday's injury occurred when Parker attempted to drive to the basket:
While things looked bleak, he initially told teammate John Henson that the ailment wasn't serious, per Gary D'Amato of the Milwaukee Journal Sentinel:
That wasn't the case, however, and the Bucks will now be without one of their brightest young stars for the rest of the season and into the 2017-18 campaign.
Parker had been enjoying his best NBA season to date with per-game averages of 20.1 points, 6.1 rebounds and 2.8 assists, all of which are career highs.
Along with Giannis Antetokounmpo, the 21-year-old forward has helped Milwaukee become one of the league's most exciting young teams.
The Bucks are currently two games out of the final playoff spot in the Eastern Conference, and making up that ground without Parker will be a huge challenge.
Outside of Antetokounmpo and Parker, Milwaukee has just one other player averaging double figures in scoring in the form of center Greg Monroe (11.0 PPG).
With Parker on the shelf, Mirza Teletovic, Spencer Hawes and fellow former No. 2 overall draft pick Michael Beasley will likely assume greater roles.