Raab, who is deputising for Johnson, said the British leader had remained stable overnight and was receiving "standard oxygen treatment".
"He has not required any mechanical ventilation or non-invasive respiratory support. He remains in good spirits and in keeping with usual clinical practice his progress continues to be monitored in critical care," Raab told a news conference.
"I’m confident that he’ll pull through because if there’s one thing I know about this prime minister, he’s a fighter. He'll be back at the helm leading us through this crisis in short order."