ESPN reported the Cowboys would host the brigade of receivers on their off day as they prepare to be without Bryant for at least one month. Bryant broke the fifth metatarsal in his right foot in the third quarter of Dallas' Sunday night win over the New York Giants and had surgery Tuesday to insert a pin into the cracked bone.
The 6-foot-3, 215-pound Butler, a seventh-round draft pick in 2013, caught 30 passes for 383 yards and two touchdowns the past two seasons with the Raiders but had difficulty climbing the depth chart.
"Now it's time to play for Americas team! #CowboysNation I'm coming!!!" Butler said on Twiter.
Nicks, 27, is the biggest name of the bunch and the player with whom the Cowboys have the greatest familiarity as a former first-round pick of the Giants. But he didn't stick with the Tennessee Titans this summer after one season with the Indianapolis Colts and wasn't signed last week after a workout with the New Orleans Saints.
Nicks failed to regain his physical form after breaking the same bone in his right foot in May 2012.
Toon, 26, played collegiately at Wisconsin and was a fourth-round pick of the New Orleans Saints in 2012. The son of former New York Jets receiver Al Toon, he was released in September with 21 career receptions for 283 yards and one touchdown.
Weems did not appear in a game for the Cowboys but was active for the opener against the New York Giants on Sunday. Brown played on the same team with Cowboys left tackle Tyron Smith at Southern California.