A U.S. appeals court on Wednesday returned a major transgender rights case to a lower court to determine whether it is still valid because the plaintiff, a student suing his school district, has graduated from high school.

The case of Gavin Grimm, a transgender boy who was denied use of the boys' room at his school in Gloucester County, Virginia, had once been set to be heard by the U.S. Supreme Court and could have been a landmark case on transgender rights.

Gavin Grimm attends Logo's 2017 Trailblazer Honors Awards show at Cathedral of St. John the Divine on June 22, 2017 in New York City. Gary Gershoff / WireImage

Grimm argued that the county school board's policy of assigning restrooms based on students' sex assigned at birth rather than gender identity was a violation of the right against sex discrimination under Title IX of the education code and the constitutional right to equal protection under the law.

The Supreme Court in March scrapped plans to hear the case and threw out the appeals court's ruling in favor of Grimm after President Donald Trump rescinded a policy protecting such youths under federal law.

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The Supreme Court sent the case back to the Virginia-based 4th U.S. Circuit Court of Appeals, which in turn remanded the case to the district court.

Had the Supreme Court ruled on the case, it could have settled one of the major civil rights disputes in the United States, whether transgender people are covered by laws designed to protect people against sex discrimination.

The Supreme Court's reversal on whether to hear the case came after the Trump administration retracted a directive by former President Barack Obama's administration telling public schools nationwide to let transgender students use bathrooms matching their gender identity.

Related: Trans Teen Gavin Grimm Slams Trump Policy at Congressional Meeting

The appeals court based its ruling on the Obama guidance and did not address the broader question of whether Grimm was protected under the federal discrimination law.

The issue of whether Title IX protects transgender students will continue to be litigated in other courts, and legal experts expect it to be decided by the Supreme Court in the coming years, possibly as early as 2018.

Other cases have been contested in North Carolina, Pennsylvania, in Illinois, Ohio and Wisconsin.

The American Civil Liberties Union, which represents Grimm, said it was disappointed in the decision.

"We'll continue to push this case forward to ensure that Gavin, and other transgender students across the country, can attend school without being stigmatized by these sorts of harmful and discriminatory policies," the ACLU said.

The case is Grimm v. Gloucester County School Board, 4th U.S. Circuit Court of Appeals, No. 15-2056.

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