The 30-year-old Donovan, the most recognisable face in American soccer, has battled minor injuries over the past half-year and has not played for the national team since September last year.
But he was called up along with 10 other players to the initial squad of 16 for the training camp in Orlando, Florida.
The squad will be trimmed to 23 players before the friendly against Scotland on May 26, the start of a busy five-game schedule for the US that includes World Cup qualifiers.
"We are excited now to get towards full numbers with (players) who are coming in with great form," Klinsmann said in a press release.
"We will continue with our rhythm of two trainings a day and see where the players are really at before we make our final decisions on the 23-man roster for the upcoming games."