But Ms Laporta's testimony raised the stakes for Mr Manafort, legal experts said.
In stunning testimony at Manafort's trial on tax and fraud charges, Gates stated he and Manafort had 15 foreign accounts they did not report to the federal government, and knew it was illegal.
In his plea deal, Gates admitted to lying to investigators a number of times, and on Monday he admitted to embezzling hundreds of thousands of dollars from Manafort's company, in the form of falsified expense reports. They have several times tried to impugn his credibility before the jury.
The trial marks the first test of the special counsel Robert Mueller's investigation into possible collusion between the president's election campaign and Russian agents.
Manafort is charged with bank and tax fraud related to political consulting work he did in Ukraine.
Mr Gates was Mr Manafort's partner in the consultancy. Both cases are connected to work Manafort and Gates did for the Ukrainian government. Gates agreed to flip on his former boss in exchange for leniency.
Gates is considered the "star witness" of the trial, which is in its second week. Testifying under immunity, she was the first witness to admit she knew accounting manoeuvres Manafort and Gates requested of her were wrong and could be crimes.
Prosecutor Greg Andres pointed out that he had created a "loan forgiveness letter between Mr. Manafort and Mr. Manafort".
Rick Gates will continue his testimony today. Instead, he glanced up at his former protege periodically but mostly stared intently at documents displayed for the jury on a screen in front of him.
Gates is expected to take more questions from prosecutors Tuesday morning, and then the defense's cross-examination is expected to take much, if not all, of the afternoon.
On Friday, a tax preparer named Cindy Laporta admitted that she helped disguise $900,000 in foreign income as a loan in order to reduce Manafort's tax burden.
Liss's testimony lasted less than 45 minutes, the shortest of any witness so far this trial.
Prosecutors are hoping that testimony from Gates, who has firsthand knowledge of Manafort's actions, will convince a jury of Manafort's guilt.
Gates also testified that a Russian citizen, who is allegedly tied to Russian intelligence, had signatory authority over some of Manafort's hidden accounts in Cyprus, according to reports.
The witness also testified he had helped the defendant file false tax returns, concealing 15 foreign accounts from the USA government despite knowing it was illegal.
He has also sought to blame Mr Gates for the crimes.
What's Gates telling the court?He also over-reported his income on mortgage and credit card applications and lied to his own personal tax accountant.
In just a little over an hour of questioning, Gates told the prosecution that Manafort directed him to open up accounts in Cyprus so that the Ukrainian politicians who paid Manafort's DMP International consulting firm for its campaign work could funnel millions of dollars to him.
He has tweeted support for his former campaign manager, suggesting he has been treated worse than gangster Al Capone.
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