Supreme Court Chief Justice William Rehnquist is moving a little slower Friday after taking a spill at his home and hurting his knee.

Rehnquist suffered a minor injury known as a "knee effusion," meaning he is experiencing some swelling underneath the kneecap along with some fluid buildup, a source close to the judge told Fox News.

He's likely to be on crutches for only a few days. In cases like his, the fluid often disperses itself, but if it continues to collect or doesn't go anywhere, Rehnquist may have to have the knee drained.

Although the 78-year-old justice had to cancel a speech at the University of Alabama law school, a court spokeswoman said Rehnquist is "perfectly fine."

Rehnquist is the court's second-oldest justice. He has served 30 years.

Fox News' Ian McCaleb contributed to this report.