American forward Jozy Altidore appears certain to miss the Copa America following yet another hamstring injury.

Altidore, who hasn't scored for Toronto in Major League Soccer this season, got hurt Saturday while taking a penalty kick against Vancouver that was saved. Toronto said Monday he will be sidelined six to eight weeks.

The 26-year-old player injured a hamstring against Jamaica in the 2011 CONCACAF Gold Cup and missed the final, then had another hamstring injury during the Americans' 2014 World Cup opener against Ghana and was sidelined for the rest of the tournament. A hamstring injury last year caused him to be out of shape for the 2015 Gold Cup, and he was dropped from the roster for the knockout rounds, where the Americans lost to Jamaica in the semifinals.

U.S. coach Jurgen Klinsmann will have to find an attacker to pair with Clint Dempsey. Possibilities on the roster include Jordan Morris, Chris Wondolowski, Bobby Wood, Gyasoi Zardes, Ethan Finlay and 17-year-old Christian Pulisic.

The U.S. also will be without a half-dozen foreign-based players for Sunday's exhibition game at Puerto Rico because of club commitments.

The Americans released their 22-man roster Monday for this week's training camp in Miami and said Pulisic will remain with Borussia Dortmund for the German Cup final on Saturday against Bayern Munich. Defender Timmy Chandler will stay with Eintracht Frankfurt for a two-leg playoff against Nuremberg on Thursday and May 23 as it tries to avoid relegation from the Bundesliga.

Defenders Ventura Alvarado (Club America), Edgar Castillo (Monterrey) and Omar Gonzalez (Pachuca) are remaining with their clubs for the Liga MX playoff semifinals, and backup goalkeeper Ethan Horvath will stay with Molde for Norweigan Tippeligaen matches against Odd on Monday and Brann on Saturday.

MLS players will report to the national team ahead of exhibition games against Ecuador (May 25 at Frisco, Texas) and Bolivia (May 28 at Kansas City, Kansas).

The U.S. must submit its 23-man Copa America roster Friday and plans to announce it the following day. The players must come from the 40-man preliminary roster chosen last month.

Seven players at this week's camp were not on the preliminary Copa roster, including five who have not previously trained with the national team: goalkeeper Zach Steffen, midfielder Caleb Stanko and forwards Paul Arriola, Amado Moreno and Fabrice Pault. The other two are midfielder Emerson Hyndman and forward Julian Green, who scored against Belgium at the 2014 World Cup.

At Copa America, the U.S. opens against Colombia on June 3 at Santa Clara, California, then plays Costa Rica four days later at Chicago and closes the first round on June 11 against Paraguay in Philadelphia.

This week's training camp roster:

Goalkeepers: Brad Guzan (Aston Villa, England), Tim Howard (Everton, England), Zach Steffen (Freiburg, Germany).

Defenders: John Brooks (Hertha Berlin, Germany), Geoff Cameron (Stoke, England), Eric Lichaj (Nottingham Forest, England), Matt Miazga (Chelsea, England), Michael Orozco (Tijuana, Mexico), Tim Ream (Fulham, England), DeAndre Yedlin (Sunderland, England).

Midfielders: Alejandro Bedoya (Nantes, France), Emerson Hyndman (Fulham, England), Fabian Johnson (Borussia Moenchengladbach, Germany), Perry Kitchen (Heart of Midlothian, Scotland), Alfredo Morales (Ingolstadt, Germany), Caleb Stanko (Freiburg, Germany), Danny Williams (Reading, England).

Forwards: Paul Arriola (Tijuana, Mexico), Julian Green (Bayern Munich, Germany), Fabrice Picault (St. Pauli, Germany), Amando Moreno (Tijuana, Mexico), Bobby Wood (Hamburg, Germany).