On Wednesday, Tottenham announced the departure of Matildas star defender Kennedy, among a raft of others, at the expiration of her contract, while Bristol City revealed Mastrantonio's exit.
Bristol, with the league's lowest budget, suffered relegation on the final day of the season, but Aussie coach Tanya Oxtoby will stay in charge for their promotion push straight back into the WSL.
Earlier this week, West Ham announced midfielder van Egmond was among eight players leaving, though fellow Matildas Tameko Yallop and Mackenzie Arnold have re-signed.
West Ham narrowly avoided relegation, finishing ninth on the ladder just three points above Bristol City, and Hammers boss Olli Harder thanked those leaving.
“I’d like to put on record my thanks to those players that will be leaving us this summer," Harder said.
"It’s been a challenging period for everyone at the Football Club as we battled relegation, but we achieved that aim and I’m thankful for that.
“We now say goodbye to a number of players, some of whom have been here since the team turned professional back in 2018.
Aussies currently remaining in the WSL include the league's top scorer Sam Kerr at Chelsea, Arsenal trio Caitlin Foord, Steph Catley and Lydia Williams, and Everton's Hayley Raso.
The departing Aussies will fight for national team places in the Matildas upcoming test against Sweden next month, prior to the Olympic Games campaign.