If Harvard had signed on to the brief filed by the 10 schools, Silverglate said, Marshall may have been forced to excuse herself from the case.
If this happened, the group of private schools--which includes MIT, Boston University and Williams College--would lose a potentially sympathetic judge on the bench, Silverglate said.
"[Harvard] didn't want to disqualify a member of the court whom it felt was probably sympathetic to it," he said.
Harvard has faced similar legal challenges in the recent past.
In July, a federal court ruled that Harvard had the right to suspend two graduating students and deny them diplomas even though they had completed all their graduation requirements.
The University's Administrative Board had found the students guilty of stealing money from Harvard Student Agencies (HSA).