Donovan, with 57 international goals, was among 30 taken into training camp but didn't make the final cut for what would have been a fourth World Cup.
The 32-year-old had insisted he wasn't a lock to make the squad for the finals in Brazil.
He didn't figure prominently in the qualifying campaign, playing in just three of 10 matches in the final round after taking a nearly four-month sabbatical from the game.
But once the veteran -- the face of football in the United States -- was included in the 30-man preliminary squad many fans were certain he'd be going to Brazil.
"To tell a player like him, with everything he's done and what he represents, to tell him 'you're not part of those 23 right now ...'" Klinsmann said yesterday. "I just see some other players slightly ahead of him.
"His disappointment is huge," Klinsmann added. "He took it very professional because he is an outstanding professional player," he added.
"But I had to make decisions as of today ... I just think the other guys right now are a little ahead of him."
They will kick off their campaign on June 16 against Ghana.
Also left off the squad was midfielder Maurice Edu. In naming the 30-man squad, Klinsmann said he saw Donovan as a pure forward rather than a midfielder. The forwards selected include young playmaker Aron Johannsson and 31-year-old Major League Soccer veteran Chris Wondolowski.
Johannsson scored 17 goals for Dutch club AZ Alkmaar last season, while Wondolowski was a hero of the US Gold Cup triumph last year with five goals in the first two matches.