On Friday, Busquets made an emotional return to the squad following a frustrating stretch in isolation, hugging coach Luis Enrique and team-mates as he arrived back in camp.
The Barcelona midfielder was removed from Spain's training base near Madrid and whisked away by ambulance on June 7, yet now he has been given the all-clear and is poised to contribute as Spain attempt to book a last-16 spot.
Busquets said he was "very happy, on a high" to learn he was healthy to rejoin the group, but recalled the sorry moment when he was told he had the virus.
"The doctor called me, he told me, and at that moment you have a lot of feelings, such as that you don't believe it, concern about what might happen, whether it could be a false positive, many things," Busquets said.
"The moment I got into an ambulance and turned for home, I went through everything. You try to be positive but in those moments it is almost impossible and you think about when you will be well, if you will be able to return, if you will get back on time.
"There are many unanswered questions that go through your head in a bad moment."
Busquets is likely to play his first match of the tournament when Spain face Slovakia next Wednesday in their final Group E game.
Speaking in a video released on the team's official Twitter page, Busquets said: "I am very grateful, not only to team-mates, but also to the president, the staff, the coach, the entire group that is in the bubble."
The 32-year-old said he had kept in constant contact with those in the Spain camp, adding they made it clear "they were waiting for me with open arms".
"I have missed you so much, you don't know how much," he told his team-mates.
"Thank you very much for all the messages worrying about me, making me feel like I was here even though I was at home. I am very proud of all of you, of the first game, of everything you are doing here and that is the way, so there is a lot left and I'm sure everything will go well."
In Busquets' absence, Spain drew 0-0 with Sweden in their opening Euro 2020 Group E game, a match in which they had 85 per cent of the possession but only five shots on target.
They play their second group game against Poland in Seville on Saturday, with Busquets expected to be a spectator after missing almost two weeks of training.
While Busquets will bolster the midfield whenever he returns to action, Spain have pressing issues in attack following the Sweden game.
They have now failed to score in two of their past three matches – having also drawn a blank in the pre-tournament friendly against Portugal earlier this month – and that is as many scoreless performances as they had in their previous 51 internationals.
Spain have not experienced successive games without finding the back of the net since 2013 at the Confederations Cup, and should they again miss out against Poland it would mean the Slovakia game becomes hugely important.