The 53-year-old former Premier League winner previously worked as Manchester City’s academy director.
The 21-year-old Briton had been boosted by winning four successive matches for the first time since her US Open title in 2021.
World number one and defending champion Iga Swiatek took her Stuttgart winning streak to 10 matches on Friday with a straight sets victory over Emma Raducanu while Marketa Vondrousova stunned three-time runner-up Aryna Sabalenka to also make the semi-finals.Vondrousova reached her first semi-final since clinching the Wimbledon title last July when she stunned world number two Sabalenka.