Both announced splits with their coaches following Wimbledon, and neither has found a new coach since then.
"There is no rush for me on the coaching side," said Muguruza, who fell to Alison Riske in the first round. "I'm just trying to go through, trying to, yeah, to be prepared for tough moments and that's pretty much it.
The two-time Grand Slam champion was with Sumyk for more than four years, winning two Grand Slams, though she brought on Conchita Martinez as a fill-in for her 2017 victory at Wimbledon.
Kerber had announced she was splitting with Rainer Schuettler, having brought on the former ATP player during the offseason. The three-time Grand Slam champion has had several coaching changes in recent years despite her success on tour.
"No, I don't have a new coach," she said, adding of her plans, "I don't know yet."
Kerber fell to Kristina Mladenovic in the first round.
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