Former Trump campaign chairman Paul Manafort may have sabotaged his own plea deal with prosecutors by lying to federal investigators in the Russia probe after agreeing to cooperate with them.

Special Counsel Robert Mueller said in a new court filing late Monday that Manafort “breached” his agreement and “committed federal crimes” by "lying to the Federal Bureau of Investigation and the Special Counsel's Office on a variety of subject matters." The filing didn't specify what matters Manafort is accused of lying about, but the claim may dash his hopes of receiving a lenient sentence.

The court filing notes that any breach “relieves the government of any obligations it has under the agreement, including its agreement to a reduction in the Sentencing Guidelines.”

Manafort is due to face sentencing in February after pleading guilty to one count of conspiracy against the United States and one count of obstruction as part of the plea agreement in September. According to that agreement, prosecutors had agreed to push for a reduction on the sentence of up to five years that each conspiracy count carries on the condition that he provide “substantial assistance.”

Manafort is also awaiting sentencing after his conviction in August in a separate case in Virginia, in which prosecutors said he could face up to a decade behind bars.

As part of his deal with the feds, Manafort also admitted to a slew of money laundering and foreign lobbying crimes and fraud crimes.

His alleged “breach” may open him up to additional charges for those offenses. The September plea agreement notes that prosecutors agreed not to bring criminal charges against Manafort for those other offenses—money laundering, false statements, tax offenses, bank fraud, and obstruction of justice—on the condition of his “full cooperation” with investigators.

Manafort has reportedly met with prosecutors at least nine times since agreeing to cooperate two months ago, providing hours upon hours of what was believed to be crucial testimony that could potentially implicate the president. While the special counsel’s office has not divulged details on what exactly Manafort is accused of lying about, Mueller’s bombshell announcement late Monday reignited speculation about whether the former political strategist could be protecting other members of Trump’s inner circle—or Trump himself.

Mueller’s office has said it will reveal more details about Manafort’s “breach” of the deal at a later date. Prosecutors are now asking a federal judge to set a sentencing date.

While both prosecutors and Manafort’s defense team signed off on the filing asking the judge to move toward sentencing, Manafort’s lawyers contended in it that he “has provided information to the government in an effort to live up to his cooperation obligations.”

Manafort, who appeared in court in a wheelchair in October and was said to be suffering from “significant” health problems, "believes he has provided truthful information and does not agree with the government's characterization or that he has breached the agreement,” the court filing said.