Richard Beeken, chief executive of the trust which runs the hospital, said a surge in patients over recent weeks had put a "huge strain" on services.
Numbers attending A&E traditionally fall following the winter period but April and May was the busiest period so far this year at under-pressure Walsall Manor. The total coming through the doors was up 14 per cent in April compared to the same time last year.
Mr Beeken said if current levels of patients are sustained it could impact on the "ability to provide a good experience for patients".
The number of patients being treated within four hours at the Manor fell to 80 per cent in April, continuing a steady decline since February when the total was 84 per cent. The national NHS target is for 95 per cent of patients to be treated within four hours.
Mr Beeken outlined his concerns in a new report to board members at the Walsall Healthcare NHS Trust.
It said: "During April and May, we have seen huge strain placed upon our urgent care services. Initial ED (emergency department) activity reports comparing April 2019 with April 2018, show an increase in attendances of 14%. This is not an occurrence that is unique to Walsall.
"Other Black Country Trusts would appear to have experienced the same. If this is sustained, this will be an unprecedented shift and will have consequent effects on our ability to provide a good experience for patients, our ability to deliver improved ED four-hour target performance and may also lead to a greater number of emergency admissions than we have planned for, with the inevitable staffing and financial consequences.
"May activity figures will be scrutinised carefully at the A&E delivery board."