The women's final between Maria Sharapova and Sara Errani should, however, take place as scheduled on Saturday.
"There is no problem with the women's final," Ysern told reporters on Friday.
"On Sunday ... it might rain in the morning until the early afternoon. We will know more tomorrow. At the moment the schedule remains the same and the men's final is planned for 1500 (1300 GMT).
"We are ready to postpone it until Monday, it is an eventuality which we have not ruled out. In that case the final would take place in the early afternoon."
World number one Djokovic and six-times champion Nadal will contest the final after both won in straight sets on Friday.
The last time the final was not played on a Sunday was in 1973 when it took place on Tuesday after a rainy end to the tournament.