Crystal Dunn (knee) out of World Cup qualifier

Crystal Dunn will miss the CONCACAF qualifiers with a knee injury. Tony Quinn/Icon SMI

KANSAS CITY, Mo. -- United States defender Crystal Dunn has been ruled out of the upcoming CONCACAF Women's Championship with a knee injury. Julie Johnston takes Dunn's place on the 20-player American roster.

Dunn sustained what U.S. Soccer termed an MCL sprain to her right knee during a training session in Kansas City on Friday and is expected to be sidelined two to four weeks. The United States begins play in the CONCACAF tournament, which serves as the qualifying mechanism for next summer's FIFA World Cup, on Wednesday against Trinidad & Tobago and must play five games in 12 days to earn one of the top three spots and an automatic World Cup berth.

"She's obviously upset," United States coach Jill Ellis said of Dunn. "But for as young as she is, she's uncommonly mature. She handled it well, as well as could be expected."

Primarily an outside back with the national team, the 22-year-old Dunn has made 12 career appearances for the United States, including four appearances and one start this year. She was expected to fill a reserve role behind starter Kelley O'Hara at left back, although that position has been among the most unsettled for United States this year.

With four career appearances for the national team, Johnston, 22, becomes the least experienced American outfield player, although in addition to being named the outstanding rookie in the recently completed National Women's Soccer League season, she was also captain of the United States team that won the 2012 FIFA Under-20 Women's World Cup and received the Bronze Ball as that tournament's third-most outstanding player.

Primarily a center back and defensive midfielder for both NWSL's Chicago Red Stars and the United States, Johnston will now be one of the puzzle pieces providing depth at outside back behind projected starters O'Hara and Ali Krieger and versatile reserve Meghan Klingenberg. Ellis also mentioned Becky Sauerbrunn, typically a fixture in the middle of the back line, as a player who could play wide if needed.

Johnston was already training with the United States in Kansas City as one of three non-roster invitees.

"She was cute; she was like, 'I'll play wherever,' which I love," Ellis said. "The reality is we have some flexibility that we can slide -- Becky's played wide for us, we've obviously got Kelley and Kling and Krieger, so we have three for two positions. And we certainly have some versatility . ... I wasn't that worried about it. More important for me, [Johnston] was in with us, and she's been doing well and I want her to continue to get experience."