Donovan's 298th and final league appearance for the Galaxy on Sunday saw the LA side win the MLS title with a 2-1 extra-time victory over the New England Revolution.
The former United States captain, and 157-time international, ended his playing career on a high, the 32-year-old bowing out with four league titles with the club.
Donovan said after revealing he would retire in August, the run-in to his final games has taken its toll.
"I'm excited, I'm pretty exhausted to be honest. It's been a long few weeks, a long month-and-a-half," Donovan told MLS' official website.
"But I'm so proud of all of us, I'm so happy for our guys. As you get older, you realise how difficult this is.
"To have this moment, is really special for all of us."
Galaxy's campaign got off to a shaky start, winning two of their first eight outings, but Donovan hailed their fighting qualities - as they overcame conceding an equaliser in the StubHub Center final as Robbie Keane struck a 111th-minute winner.
"It's been a pretty trying season, we weren't great to start then we went through a really good run at the end," Donovan said.
"The thing about our team is we're pretty resilient, ups and downs, we stay pretty even keel.
"And today I think New England were probably the better team for long stretches of the game, but we know how to win, and in tough moments, we have guys who make plays, and today they did."
