With forward Mallory Swanson sidelined by a serious knee injury for the foreseeable future, the United States is facing some uncertainty as it prepares for the Women's World Cup.

How will the U.S. replace one of its best players?

“I think that in this past year, you’ve seen a lot of players go down with injury and we’ve been able to adapt,” forward Lynn Williams said. “I think that’s what the team’s going to continue to do, is continue to adapt. Mal’s absence is a huge hole to fill, but we have amazing players on this team and we’re going to figure out a way to do it.”

Swanson tore the patellar tendon in her left knee during a 2-0 exhibition victory over Ireland on Saturday, throwing her availability for soccer's biggest tournament this summer into doubt since there is no official timeline for her return. She was the team’s leading scorer this year with seven goals and a six-game scoring streak, tied for fourth longest in team history.

Swanson said in an Instagram post that she had surgery Tuesday morning.

“This is hard,” she wrote in a post that included a photo of her smiling with arms raised on the field in her U.S. jersey. “I'm in shock and don't have much to say other than thank you to everyone for the messages. I feel the love and prayers, and holding them close to my heart.”

Williams and Trinity Rodman are among the players coach Vlatko Andonovski will look at to fill the void left by Swanson's absence. Also in the mix is Megan Rapinoe, who is injured and was not with the team for its 1-0 victory over Ireland on Tuesday night.

“No matter who gets injured it is a tough moment because their careers, their futures are impacted, and the team is impacted," Andonovski said. "Mal is arguably one of the best players in the world. It’s unfortunate what happened but I think that the team is doing well and they do galvanize and bond around unfortunate things like this.”

Swanson was injured in the 40th minute of Saturday's game after contact with an Irish player, crying out in pain as she fell to the ground. She was carted off the field but Andonovski said she optimistically told him: “Coach, I'm fine, I'll be good.”

“Mal wants us to move on and be successful and do right by her,” he said Monday.

Swanson, 30, returned to Chicago, where she plays for the Red Stars of the National Women’s Soccer League. Formerly known by her maiden name Pugh, she married Chicago Cubs shortstop Dansby Swanson in December.

Alyssa Thompson was hastily brought to St. Louis to take Swanson's place among the 26 players called up for the two matches against Ireland. The 18-year-old was the top pick in the NWSL draft out of high school by Angel City.

Thompson, who has already made a pair of appearances with the national team, was at practice with Angel City when she got the text. Her mom packed her suitcase and she barely made her flight because of traffic in Los Angeles.

“I'm just happy to be here, and I can control what I can control,” Thompson said. “I'm just going to to put my best foot forward and see what happens.”

The matches against Ireland are the last for the United States before Andonovski selects a roster for the World Cup, which will start in late July in Australia and New Zealand. The United States is the two-time defending World Cup champion.

“We all understand that we have a job to do past this now and we’ve got to prepare for the World Cup,” Andonovski said. “We've got to prepare and we’ve got to do a job. And if there’s a team that has a group of players ready to step in in the moment, that's this team.”