Christine, who is engaged to footballer Frank Lampard, is expected to continue hosting the programme five days a week, while her co-star Adrian Chiles will move to a four-day week from September.
A spokesperson for the morning series confirmed that Chiles signed a contract in 2010, stating that he would present Daybreak from Monday through to Thursday in the second year of the show.
But they declined to comment on who would be stepping into his shoes in September.
Meanwhile, those close to Grainne (37) have revealed how her agent is currently in negotiations with the station about a new role for her on the series this autumn.
It was confirmed this week that the mum of one will not be returning to the couch in her former capacity of features editor.
But a source close to the presenter told the Herald: "Grainne is by no means finished with Daybreak for good.
"Nothing has been confirmed about her role in the autumn yet, but there are a few different possibilities on the table.
"One idea is that she may be lined up to take over from Adrian on Fridays.
"This would tie in perfectly with her other projects with RTE, but producers are concerned that she and Christine may not have the right chemistry together.
"There are big changes coming into place with Daybreak in the autumn. No-one knows what's going to happen yet or if it will even be back in the same guise, but Grainne's agents are working hard to ensure she's part of the line-up," they added.
An ITV spokesperson confirmed that they hope to work with Grainne again but did not elaborate on what role, if any, the broadcaster will have in the second season.
"Grainne Seoige will not be continuing in her role as features editor on Daybreak," the representative told the Herald.
"She remains a friend of the show and we hope to see her on the sofa again in the future," they added.
It has been speculated that the show could be axed, moved to a later time slot or even revert back to its previous GMTV format.