The Australian shot-stopper has been called in by United to replace Josh Wicks who is out for four to six weeks with a shoulder injury.
Sharpe told tribalfootball.com that he will head to DC in a week or so and is looking forward to linking up with former Colorado teammates.
"(I) Got the call on Tuesday that I was leaving Thursday, for the game Saturday," Sharpe said.
"I am heading back to Denver today for a week and then will head back out to DC in about a week for the last two games (as) DC have a bye week next weekend.
"I am in the hotel, training was good on Friday, however we had a tough loss last night to Chivas 2-0, which is going to make getting into the playoffs very tough now for the team.
"Johnny DiRamondo and Christian Gomez I know really well both used to play with me at Colorado. Josh Wicks and Ely Allen I know from my time at LA Galaxy. (It) has been great to see all these guys."