A close associate of Trump is set to appear before a grand jury in New York City

On Monday, a New York grand jury is set to hear from Robert Costello, a lawyer who is allied with former US President Donald Trump.

Costello was asked to testify by the Manhattan district attorney’s office, who is investigating hush money payments made during Trump’s 2016 presidential campaign.

Costello has reportedly raised concerns about the credibility of key witness Michael Cohen, who had previously acted as a lawyer and fixer for the Trump Organization.

It is unclear whether Costello’s testimony could impact the grand jury’s ongoing investigation.

The district attorney’s office declined to comment on the matter.

Trump has recently criticized the investigation and expressed concern that he could face criminal charges.