Gil is nursing a hamstring knock that has kept him out of action for Real Salt Lake's past two matches.
Columbus' Trapp (above), meanwhile, is listed with a groin injury after going the full 90 in Columbus' 1-1 draw with D.C. United. The 20-year-old supplied the long lead pass that led to Hector Jimenez's 90th-minute equalizer.
The US U-21 roster is now set for 19 players for the camp, which started Sunday and runs through Thursday in Carson, Calif. US Under-20 national team head coach Tab Ramos is overseeing the five-day camp that includes a core group of players who will make up the majority of the U-23 men's team that will attempt to qualify for the 2016 Olympics in Rio de Janeiro, Brazil.
The camp also consists of an international friendly match against Club Tijuana on Wednesday.
Roster By Position:
GOALKEEPERS (2): Jonathan Kempin (Oklahoma City Energy; Leawood, Kan.), Kendall McIntosh (Santa Clara; Santa Rosa, Calif.)
DEFENDERS (5): Christian Dean (Vancouver Whitecaps FC; East Palo Alto, Calif.), Juan Pablo Ocegueda (Tigres UANL; Riverside, Calif.), Shane O’Neill (Colorado Rapids; Boulder, Colo.), Dillon Serna (Colorado Rapids; Brighton, Colo.), Oscar Sorto (LA Galaxy; Los Angeles)
MIDFIELDERS (5): Alejandro Guido (Club Tijuana; Chula Vista, Calif.), Marlon Hairston (Colorado Rapids; Jackson, Miss.), Benji Joya (Chicago Fire; San Jose, Calif.), Collin Martin (D.C. United; Chevy Chase, Md.), Esteban Rodriguez (Club Tijuana; Bell Gardens, Calif.)
FORWARDS (7): Daniel Cuevas (CF Lobos BUAP; Sacramento, Calif.), Danny Garcia (FC Dallas; Dallas), Jack McBean (LA Galaxy; Newport Beach, Calif.), Jordan Morris (Stanford; Mercer Island, Wash.), Sean Okoli (Seattle Sounders FC; Federal Way, Wash.), Victor Pineda (Chicago Fire; Bolingbrook, Ill.), Jose Villarreal (Cruz Azul; Inglewood, Calif.)