Rizzo told The Washington Post in a text message that Harper "is not going anywhere." He also told ESPN's Buster Olney that Harper will not be dealt.
The Nationals (52-53) are 5½ games behind the first-place Philadelphia Phillies in the NL East, leading to widespread speculation that they would consider trading Harper before Tuesday's 4 p.m. ET non-waiver deadline.
ESPN confirmed reports from multiple outlets Monday that Washington spoke to teams to determine what type of return package the Nationals might receive if they were willing to trade Harper.
Rizzo apparently ended that chatter Tuesday morning, telling the Post, "I believe in this team."