The BBC Radio 1 drivetime DJ - who lives with dancer Meshach Henry - has been on holiday for the past three weeks but was due to return to the air on Monday August 31.
However, as a member of his household has been in contact with COVID-19 he must now self-isolate for two weeks.
Grimshaw, 36, revealed on Instagram: “Sooooooo... this morning Mesh found out that he has to self isolate for the next 14 days and as I live with him, cos I really like him, so do I. Obviously livid.
“So gutted but rules are rules and CBA [can’t be arsed] starting a second spike in the Live Lounge. Both feel totally fine right now and have no symptoms. Fingers crossed we like each other for 14 more days. Hope everyone is happy and healthy.”
Dev Griffin has been filling in for Grimshaw while he was on annual leave from Radio 1 for the last three weeks. It is rumoured BBC bosses may be working on a way for Grimshaw to host his show from home.
During his time off he and Henry enjoyed a romantic holiday in Paris. In July, Grimshaw took part in a socially distanced series of Channel 4 reality show Celebrity Gogglebox, along with his niece Liv.
Grimshaw has been dating 23-year-old dancer Henry since 2018. They moved in together in July 2019.
The radio DJ had previously struggled to find love as getting up early to present Radio 1’s breakfast show made dating difficult. But he met Henry after moving to the drivetime show in August 2018.