Zeman had just been discharged from a Prague hospital where he had been in care for six weeks.
Czech president Miloš Zeman has immediately returned to hospital after testing positive for COVID-19.
The president's office confirmed on Thursday that Zeman would return to the military university hospital in Prague.
The 77-year-old had earlier been discharged after spending more than six weeks in care and had planned to recover at his presidential residence in Lany Castle.
But his spokesperson confirmed that Zeman had tested positive for coronavirus after arriving at the castle.
"The President's programme will be suspended during the treatment for COVID-19," a statement read Zeman had been set to swear in the new Czech coalition government led by Petr Fiala on Friday.
President Zeman was initially admitted to intensive care on October 10, one day after the Czech parliamentary elections.
Zeman — a heavy smoker and drinker who has suffered from diabetes — has trouble walking and has been using a wheelchair. His condition was attributed to an unspecified chronic disease.
The Prague hospital said earlier on Thursday it would have preferred Zeman to remain at the facility, but accepted his decision to leave due to a “significant improvement”.
But Zeman has now returned to the hospital to "resolve this situation," his spokesperson said.
With the president remaining in hospital, the swearing-in of the new government will now be delayed.
A three-party, liberal-conservative coalition known as Spolu, or "Together" — composed of the Civic Democratic Party, Christian Democrats, and the TOP 09 party — won the election with a 27.8 per cent share of the vote.
Spolu teamed up with a liberal coalition made up of the Pirate Party and STAN — a group of mayors and independent candidates — which came in third place with 15.6 per cent of votes.
The new partnership will hold 108 seats in the 200-seat lower house of the Czech parliament, relegating populist prime minister Andrej Babiš and his centrist ANO (YES) movement to the opposition.
Zeman had accepted Babiš' formal resignation on November 11, after he was moved from intensive care.
The 77-year-old president has fifteen months remaining in his second and final five-year term.