Scrum-half Youngs picked up a minor thigh injury in Leicester Tigers' win over Gloucester, while Worcester Warriors centre Lawrence, 22, is unwell.
The injury to 32-year-old Youngs is not expected to rule him out of Leicester's game against Saracens on Saturday.
England are preparing to face Tonga, Australia and South Africa in November.
Eddie Jones announced his 45-man England squad a week ago with big names such as Billy and Mako Vunipola, Jamie George and George Ford all left out.