"And I say, 'How's the crowd going to be?' And, you know, it's like you don't have a crowd".
"You had a pitch that broke a lot of bats", Trump told the retired New York Yankees relief pitcher after they had thrown several balls while a number of Little League youth baseball players observed and played catch.
It comes after Mr Trump revealed at a press conference Thursday that he will be throwing out the first pitch at a Major League Baseball game.
Many local officials have prohibited teams from welcoming crowds into sports stadiums during the coronavirus pandemic.
Trump noted that there will be no fans in the ballpark that day, unlike when Rivera used to make his dramatic entrances.
United Kingdom government secures 90 million doses of Covid-19 vaccines
The trial showed that volunteers given two doses of the vaccine produced virus-neutralizing antibodies, similar to the USA trial. In early June, the team was forced to begin trials of the vaccine in Brazil and South Africa, where cases were rising quickly.
"We ask all Americans to exercise vigilance, practice social distancing, wear a mask, do whatever is necessary so we get rid of this terrible situation", Trump said at a press briefing late Thursday afternoon.
The White House has said that Trump is regularly tested for COVID-19, and normally requires reporters and others to be tested before they come into close contact with the president.
The President of the United States as well as the children are seen in the footage not wearing any face coverings or practising social distancing, just hours after Mr Trump urged American citizens to practice social distancing and wear masks.
Major League Baseball is opening its season Thursday.
The Yankees confirmed Trump's comments on Thursday night, according to reports. "And we ask all Americans to exercise vigilance, practice social distancing, wear a mask, do whatever is necessary so we get rid of this disgusting situation, this frightful disease". "I think setting the example is very important". "The key is to get back to normal".