Several senior members of O'Neill's squad had reportedly pencilled in a day at the races down in Gloucestershire but decided against it as the Black Cats continue their battle to avoid the drop.
Sunderland are 15th in the Premier League table - just six points clear of the relegation places - as they prepare for a crucial home game against Norwich on Sunday.
O'Neill said: "Initially, they had asked for it, as they had done for the last number of years, and it's fine.
"But when you are looking at some results, enjoyment can come later. Let's go and win some matches first, that would be the most important issue.
"The players do understand - I think they have always done that. Since I have come into the football club, they felt the same a while back.
"We need to win some matches - it's vitally important that we do. We have still a number in which to do so and we have got points to play for.
"My own view is that it was the proper thing to do."