The English supermodel, who dated Mr Depp in the 1990s, is expected to appear in court by videolink later this week.
Mr Depp is suing Ms Heard over a 2018 article she wrote in the Washington Post, which his lawyers say falsely implies he physically and sexually abused her while they were together.
He has denied all accusations.
A source close to Mr Depp confirmed to the PA new agency that Ms Moss will give evidence on Wednesday by videolink.
The news comes in the final week of the US trial, taking place in Fairfax County, Virginia, with closing arguments expected on Friday.
Mr Depp has refused to make eye contact with Ms Heard during the three days she has been giving evidence.
Long queues continued to appear outside the courthouse, with some members of the public having queued overnight for a chance to get into the courtroom to observe the proceedings.
Mr Depp has already given evidence and faced cross-examination and has alleged that he was a victim of domestic abuse during the relationship.