Colliver took charge of the Sheepicorns alongside Mark Ward in the 2021/22 season and finished the campaign in ninth.
However, the West Yorkshire side are yet to find their feet this season.
Ossett are currently sitting 13th in the NPL East Division, having only won three of their opening 10 games.
The club have announced that there will be more information in regards to who will take over, within the coming days.
Photo credit Ossett United
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