Sergino Dest isn't quite irreplaceable for the United States men's national team, but his unique skillset is. Dest' ability to dictate games as an attacking fullback is impossible to teach, and there isn't another player in the USMNT player pool that can do what he does at the right-back position.
And that's what makes Dest's knee injury, which is set to rule him out for up to nine months, so heart-breaking for the USMNT. It's not that they can't replace him with a capable backup, because they can. There are other good right backs in the player pool. There are, though, no players quite like Dest. There aren't any players capable of making game-breaking moments from that spot on the field and no players that have his ability to effortlessly weave his way into the attack.
The U.S. has survived without him before, of course, and there are players that will be ready to step into the void and make their own mark on the Copa America this summer. Losing Dest, though, is a big, big blow that will force Gregg Berhalter to rethink his tactics ahead of the upcoming tournament on home soil.