Mogulof said that late Sunday a man managed to climb up a tree that's apart from the tree where the other three protesters are staying.
University officials think the new protester may not stay in the tree very long because he may not have many supplies and because he's isolated from the others, Mogulof said.
A supporter of the tree-sitters was arrested Sunday at a rally in which supporters were trying to provide food, water and other supplies to the people who are still in the trees, Mogulof said.
Mogulof said university officials prevented the supporters from providing the supplies because they have a court order barring the tree-sitters from being in the tree.
"We're just enforcing the law," Mogulof said.
Protesters have been living at the grove of trees since Dec. 5, 2006, when a UC Board of Regents committee approved building a training center next to the football stadium. The project calls for tearing down the trees.
The project has been on hold since Alameda County Superior Court Judge Barbara Miller issued a preliminary injunction against it in January 2007. Miller issued a mixed ruling on the case two weeks ago and will have another hearing on July 17.
Doug Buckwald, a spokesman for the tree protesters, said 50 to 60 supporters of the tree-sitters came to the grove of trees Sunday to try to provide supplies.
Buckwald said that although university police prevented most supplies from getting through, supporters managed to float a balloon containing supplies up to the tree-sitters.
However, Buckwald said the amount of supplies that got through was "insignificant."
Buckwald said his biggest concern now is that the tree-sitters have enough water to safely get through the heat wave that's forecast for the next several days.
"Water will be the big issue for everyone the next few days," he said.
Buckwald said the remaining tree-sitters "have been through a lot and are already stressed."