Leicester Royal Infirmary's accident and emergency department was almost the worst performing in the country during January, according to a new report.
Emergency doctors failed to see and treat 2,620 patients within the four-hour target time set by the Department of Health.
Under the rules, 95 per cent of patients must be seen within the time slot – but at the infirmary doctors managed 85.1 per cent.
In a report to directors at Leicester's hospitals board meeting, Jeremy Tozer, interim director of operations, said: "January was the worst performing month to date.
"As of February 3, the University Hospitals of Leicester NHS trust was ranked 142 out of 144 acute trusts over the past four weeks, with a performance of 85.1 per cent."
Mr Tozer said the poor performance was down to nearly 500 more patients compared with the same time last year arriving for treatment.
An increase in staff sickness, which meant having to close extra beds, had also impacted on the infirmary's ability to move patients from the A&E department and on to wards.
Mr Tozer said that by the end of March, it was predicted 168,615 patients would have been through A&E in the past year.
This will be 6,647 more than the previous year and represents an increase of 4.2 per cent.
Mr Tozer said work to try to "divert" patients to the nearby urgent care centre had not had a significant effect on reducing the work load in A&E.
However, changes from the start of last week should help improve the time in which patients are seen.
It includes speeding up assessment with the creation of a new joint clinical team.
The number of ward rounds on the rapid assessment, short stay assessment and clinical decisions units have been increased and new patients seen within half an hour.
Mr Tozer said: "In the first week we implemented the changes we achieved 95 per cent performance in A&E on two days. This week has been tough again but the system is proving beneficial to the times patients are being seen."
Leicester's hospitals face penalties of about £700,000 a month for not meeting the 95 per cent target.
However, the Leicester City clinical commissioning group (CCG), which will take on responsibility for running local health services in April, has said it will give the infirmary £150,000 a week for each week it meets the target.
The CCG is also working on a review of ambulance requests from GPs to see if all patients need to go to hospital.
Mr Tozer said: "The impact of this work seems very positive."
Zuffar Haq, of the Leicester Mercury Patients' Panel, said: "The hospital needs to improve its system in A&E so patients are looked after quicker and better."
