SAN JOSÉ, Costa Rica — No player has scored more goals for the United States men’s national team than Landon Donovan, and six months after his 31st birthday, he insists that he has never performed better on a soccer field than at this moment.

And yet, as the United States prepared to resume its World Cup qualifying campaign on Friday night against Costa Rica, Donovan’s role in the squad remains nebulous.

The Americans have coursed through their first six qualifying matches, earning 13 points and all but ensuring their spot at the World Cup in Brazil next summer. But thus far, Donovan has played no part. After he spent his winter on a self-prescribed sabbatical, he was excluded from Coach Jurgen Klinsmann’s early rosters, and his future with the national team seemed in doubt.

When Donovan’s name appeared on Klinsmann’s latest roster last month, it seemed to raise more questions than it answered: How might he be deployed? How would he integrate into a group that has done well without him? These were questions the player, the coach and the team seemed eager to address.