Lerner told Grant Paulsen and Danny Rouhier of 106.7 The Fan that the Nats presented the outfielder with their best offer in September and have since shifted their focus elsewhere.
"But I really don't expect him to come back at this point," he said. "I think they've decided to move on. There's just too much money out there that he'd be leaving on the table. That's just not [agent] Mr. [Scott] Boras' MO to leave money on the table."
Bob Nightengale of USA Today reported the Nationals' offer to Harper included an annual base salary around $30 million as part of a long-term extension proposal.
Lerner didn't confirm the amount, but he told Paulsen and Rouhier the club made it clear to the outfielder's representation they wouldn't be interested in joining an offseason bidding war.
"Well, when we met with them and we gave them the offer, we told them, 'This is the best we can do.' We went right to the finish line very quickly," Lerner said. "And we said, 'If this is of interest to you, please come back to us and we'll see whether we can finish it up.'"
He added it's now a "strong possibility" the Nats wouldn't be able to make a deal work even if Boras came back with interest in the original offer because of their other moves.
Washington signed starting pitcher Patrick Corbin to a six-year, $140 million contract (via Jamal Collier of MLB.com) while acquiring two relief pitchers, Kyle Barraclough and Trevor Rosenthal, and two catchers, Kurt Suzuki and Yan Gomes, via trades and free agency.
General manager Mike Rizzo previously said he felt the blockbuster Corbin signing was "independent" of the Harper situation and wouldn't rule out a reunion, per Chelsea Janes of the Washington Post.
If the Nats don't add another outfielder, top prospect Victor Robles will likely join Adam Eaton and Juan Soto in the Nationals outfield to open the 2019 season.
Meanwhile, Tim Brown and Jeff Passan of Yahoo Sports reported officials from the Chicago White Sox, New York Yankees and Philadelphia Phillies were among the "upward of a dozen teams" to meet with Harper or make plans to do so during free agency.