Fabian Johnson, left, vying for a ball against Schalke’s Thilo Kehrer in a match for Moenchengladbach, injured his hamstring and was replaced on the U.S. national team roster by Graham Zusi. (Ralph Orlowski/Reuters)

The U.S. national team has begun to gather in San Jose without three probable starters for two vital World Cup qualifiers.

Forward Bobby Wood was the latest scratch, withdrawing Sunday after injuring his back in a Bundesliga match the day earlier. Fabian Johnson, a midfielder and defender, went down with a hamstring injury on Thursday, the day after new coach Bruce Arena set his 24-man roster.

Defender DeAndre Yedlin didn’t even make it as far as the initial list: His thigh ailment removed him from consideration.

Defender Eric Lichaj, an option at the outside back positions, also dropped out of the running with an injury and goalkeeper Brad Guzan, in a battle with Tim Howard for the starting job, stepped away Thursday because the timetable for his wife to give birth changed.

Arena replaced Guzan with David Bingham, a San Jose Earthquake who will inherit the No. 3 slot behind Howard and Nick Rimando. Graham Zusi took Johnson’s roster slot. Sacha Kljestan, a surprising omission from the initial roster announcement, was summoned for Wood.

Needing defensive reinforcement, Arena also summoned veteran Matt Besler on Sunday, raising the count to 25 players for Friday’s qualifier against Honduras at San Jose’s Avaya Stadium and the March 28 visit to Panama.

Arena has two players more than needed to suit up for an international match because of two games in a short period of time and Jermaine Jones’s yellow-card suspension for the Honduras encounter.

The roster shuttle and loss of key players are hardly the optimal build-up to Arena’s first training camp involving all eligible players. (With European- and Mexican-based candidates tied to their club schedules, the winter camp featured almost all MLS candidates.)

Of the several absences, which ones hurt the most? Johnson and Yedlin.

Johnson is a high-performing figure with Bundesliga side Moenchengladbach, a standout at the 2014 World Cup and a multi-tasker for the national team. Had he been available, Johnson would’ve started at left wing, left back or, in Yedlin’s void, right back.

Yedlin would’ve started at right back, the position at which he has excelled with Newcastle, which is in the hunt for promotion to the Premier League.

Without Johnson, Yedlin and Lichaj, Arena will have to turn to someone whose best position is not right back (Geoff Cameron and Michael Orozco) or is learning the role (Graham Zusi, a former midfielder).

Wood’s withdrawal damages frontline muscle. He seemed likely to partner with Jozy Altidore. Wood, 24, has scored nine goals in all competitions for relegation-threatened Hamburg this season and three in 2018 World Cup qualifiers.

Will Arena leave Altidore on his own, or pair him with Jordan Morris or Clint Dempsey?

Amid the roster turmoil, several players can Arena peace of mind.

Altidore posted a goal and assist in Toronto FC’s 2-0 victory at Vancouver on Saturday. Christian Pulisic, the 18-year-old wonder from Hershey, Pa., has started three of the past four matches for Borussia Dortmund and, in the past two weeks, scored in the UEFA Champions League, Bundesliga and German Cup.

In England, Cameron has regained a Stoke City starting job, albeit in defensive midfield, since returning from a four-month injury layoff. John Brooks and Omar Gonzalez, the top candidates to start in central defense, start every weekend for Hertha Berlin and Pachuca (Mexico), respectively.

FC Dallas midfielder Kellyn Acosta, right, tries to dribble past Pachuca defender Omar González during the second half of a recent CONCACAF Champions League semifinal match. (Jeffrey McWhorter/Associated Press)

FC Dallas defensive midfielder Kellyn Acosta, 21, is rapidly emerging as one of MLS’s top young talents.

Howard, a two-time World Cup starter, is back in form with the Colorado Rapids after returning from groin surgery in November.

With all of the shuffling, only four players have arrived from Europe: Brooks, Pulisic, Cameron and defender Tim Ream. Three are from Mexico: Gonzalez and defenders Michael Orozco and Jorge Villafaña, a candidate to start at left back, despite limited international experience. The other 18 come from 13 MLS clubs.

The United States lost the first two final-round qualifiers under Arena’s predecessor, Jurgen Klinsmann, and sit last in the six-nation standings with eight matches left. Three teams will earn automatic berths in the Russian-hosted World Cup. A fourth will enter a playoff against an Asian team next fall.

The Americans have participated in every World Cup since 1990.

Honduras (three points from two games) will arrive in San Jose with five MLS players, including three from the Houston Dynamo, and former D.C. United star Andy Najar (Anderlecht, Belgium).