"After a great deal of thought and given my family circumstances - three young children, including a newborn, and a mother at high risk - I have decided not to participate in the 2020 season," Zimmerman wrote Monday in a statement published by CAA Baseball.
The 35-year-old added that he is not retiring yet but has not decided on his future in baseball beyond this year.
Zimmerman told The Associated Press on Friday that he was still weighing his options for the season.
"When it comes down to it, it's a decision not just for me, but for my family as well," the two-time All-Star said.
"I have a 3-week-old baby. My mother has multiple sclerosis and is super high-risk; if I end up playing, I can pretty much throw out the idea of seeing her until weeks after the season is over.
"There's a lot of factors that I and others have to consider. I don't think there's a right or wrong answer; it's everybody's individual choice."
Nationals right-hander Joe Ross has also elected not to play this season, Britt Ghiroli of The Athletic reports. Two or three other Nationals players are reportedly still deciding if they will play or not.
Washington general manager Mike Rizzo said the team supports players' decisions to focus on family during the COVID-19 pandemic.
"We are 100 percent supportive of their decision to not play this year. We will miss their presence in the clubhouse and their contributions on the field," Rizzo said, according to Ghiroli.
All players have the option to sit out the shortened 2020 season, but only those determined to be at a high risk of contracting the disease caused by the coronavirus will reportedly receive full prorated pay and service time.
A high-risk player who opts out will have the option to rejoin his team later in the campaign if the team physician and an MLB joint committee approve, according to Jayson Stark of The Athletic. Players not deemed to be high-risk will reportedly be ineligible to return during the regular season or playoffs.