Officials at the British Horseracing Authority are hoping to make a decision on Monday evening as to whether racing can resume on Wednesday following a six-day shutdown due to equine flu.
The BHA estimated upwards of 700 negative tests were processed on Sunday and are continuing to work through the thousands of samples sent from stables as the sports seeks a swift return to action.
David Sykes, director of Equine Health and Welfare for the BHA, said: "The data is encouraging and provides a further indication that the precautionary safety measures have helped to contain the spread of disease.
"However, the picture is still developing and it remains the case that we will make an evidence-based decision about the situation on Monday.
"It remains paramount that, for the sake of our horse population, we do not take any unnecessary risks. This is not a common cold, it is a highly contagious and potentially serious disease."