Instead of del Ponte, the prosecution will be represented by Prosecutor Alex Whiting, the same source said.
Del Ponte left for Washington, where on Tuesday and Wednesday she will meet US officials at the State Department and Congress.
On Thursday, del Ponte will submit a regular six-month report to the UN Security Council, as will the President of the International Criminal Tribunal for the former Yugoslavia (ICTY), Fausto Pocar.
General Gotovina will enter a plea to the charges in his indictment before Judge Carmel Agius of Malta and not before Judge Kevin Parker as was announced previously, ICTY spokesman Jim Landale confirmed, adding that there was a possibility for the indictment to be read out in full if Judge Agius decided so.