LEEDS, England (AP) — Leeds midfielder Tyler Adams will miss an undetermined amount of time with a hamstring injury, and manager Javi Gracia said the American won’t be easy to replace.

The 24-year-old Adams was ruled out of Leeds’ match at Wolverhampton on Saturday after sustaining the injury this week in training. The United States captain will also miss upcoming games with his national team.

“Tyler is different than others. There is no one like Tyler,” Gracia said of the defensive midfielder on Friday.

The Spanish manager offered no timetable for Adams’ return as the club battles to stay in the Premier League.

“Tyler is injured and in this moment he’s with a specialist and we’ll see how long he’s out of the team,” Gracia said. “We have other players. All of us know that Tyler is a key player for us but we have to manage with the squad we have.”

Weston McKennie and Marc Roca are options to fill in, as are 19-year-old Darko Gyabi and 17-year-old Archie Gray, Gracia said.

“These are the players that are usually training with us in that position,” the former Watford manager said.

Leeds is one spot above last-place Southampton but the bottom six teams are separated by only three points.