Landon Donovan in action

CARSON, Calif. – Clint Dempsey returned to Major League Soccer with great fanfare, but the US national team captain hasn't had the expected impact since signing in August with the Seattle Sounders.

Landon Donovan understands why.

“I think Clint's had a lot to deal with, and a lot more than people realize,” said the LA Galaxy star, who will face off with his US teammate for the first time in MLS since 2006 in a critical end-of-season showdown Sunday evening in Seattle (9 pm ET, ESPN). “And I don't think people understand how difficult it is to have that sort of pressure on you to become the face of the league so quickly, and to have so much pressure on you to perform, and it's not easy.

“He's dealing with that as well as he's been dealing with injuries, he's learning to play on [Seattle's artificial] turf, he's probably getting used to the travel again, which is all part of it. All these things add up to making it very difficult.”

Dempsey has played in eight matches with the Sounders, five of them starts, without contributing a goal or assist. He's been slowed by a series of injuries, with his shoulder ailment coming of the heels of a hamstring strain that kept him out of the Sept. 21 clash with the Galaxy, a game Donovan also missed because of injury.

“We all know Clint is a very good player,” Donovan said, “and I think that [as soon as] he hits the net once, things will change. It's only a matter of time till that happens.”

They've played together on the national team for nearly a decade but have faced off just five times, and not in an MLS game since opening weekend of the 2006 season, when Dempsey played for New England. And they're the top two scorers in US history – Donovan has 57 goals in 158 appearances, Dempsey 36 in 101.

It adds a lot of buzz to a showdown that has much to say about the Western Conference playoff race, with the winner – or LA with a draw if Colorado fails to beat Vancouver – avoiding a Knockout Round game next week.

“I don't really look at it that way,” Donovan said about the tête-à-tête with Dempsey. “For us, it's an important game. It'll be fun. It will add some drama, I'm sure, for other people, but for us it's a game we need to win, and I'm sure they see it the same way.”

Donovan has gotten the best of their rivalry over the years, beating Dempsey and the Revolution in April 2004 with San Jose and in the 2005 MLS Cup final with the Galaxy. There was a draw at New England in July 2005, and the Revs won that 2006 opener in Southern California.

The success has come even outside of MLS. Donovan, while on loan to Premier League side Everton, set up two goals in an FA Cup fourth-round win over Dempsey and Fulham in January 2012.

Dempsey's decision to leave England and sign on Aug. 3 with the Sounders was “very important” for MLS, Donovan said.

“I think the more players we have here that are part of the national team – in his case, the captain of the national team – I think it's better for all of us,” Donovan said. “We're slowly still building this league into what we want it to become, and having players of his caliber here helps a lot.”