BEIJING — One of China’s most prestigious universities has suspended a law professor and placed him under investigation after he published a series of essays that warned of deepening repression under President Xi Jinping, he said on Tuesday.

Professor Xu Zhangrun, of Tsinghua University in Beijing, shot to prominence last year when he published a passionate essay in July that was a rare rebuke of Mr. Xi’s rule. The essay denounced Mr. Xi’s authoritarian tendencies as driving China back to closed, repressive politics that could prove disastrous for the country.

In spite of censorship, the essay spread in China, capturing a current of disquiet about the direction of the country. Professor Xu received warnings, but he kept publishing pieces that criticized the authorities’ intolerance of dissent.

Now, as if to prove Professor Xu’s point, the ruling Communist Party seems to want to silence him.

His fate will be closely watched as a measure of how far the party under Mr. Xi will go in tightening restrictions over Chinese academic life, which is already heavily controlled. Since Mr. Xi came to power as party leader in 2012, he has taken particular aim at legal ideas, like constitutional limits on power, that he warned could be used to weaken party control.