The Broncos also signed defensive end Gerald Rivers to their practice squad Wednesday.
Barrett is an undrafted rookie from Colorado State who spent the last six weeks on Denver's practice squad.
Barrett started 35 of 38 games at CSU, collecting 246 tackles, 18 sacks, 32 1-2 tackles for loss, three interceptions, six pass breakups, seven forced fumbles, four fumble recoveries and three blocked kicks.
Trevathan is on recallable IR with a broken bone near his left kneecap. He's not eligible to return until mid-December.
Rivers, undrafted out of Ole Miss, played in two games for the Rams and Jaguars last season.
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