Jennings said Guyon Espiner, who reports for 60 Minutes, may have a presenting role on the second news and current affairs show that is in development.
Espiner declined to comment and TV3 said planning for the second show was in the early stages.
Jennings said McRoberts had "a very good skill set", but as a presenter he did not fit with the new shows.
"We want to signal that the new show is very different," he said.
McRoberts will also continue to front the overseas news show 360.
Jennings said the programme replacing 60 Minutes would be "more flexible", and the second show would also be "very different".
TV3 is backing another series of the weekend current affairs show The Nation, presented by Rachel Smalley.
Garner steps down as political editor at the end of next month to host the drive-time show on TV3's sister radio station RadioLive.
"I'm keen to keep him involved," Jennings says.