Both Udoka and Collins were vying for the 15th spot, which went to draft pick Patty Mills, who is out with a broken foot.
Udoka has played five seasons in the NBA, including a previous stint in Portland. He averaged 6.8 points, 3.4 rebounds and 18.8 minutes in five preseason games.
Collins, who played eight years with the Utah Jazz, played in four preseason games with an average of 3.5 points, two rebounds and 14 minutes.
Meanwhile, there was no official word Thursday whether the Blazers and forward LaMarcus Aldridge had signed a contract extension.
A person close to the situation who spoke on the condition of anonymity because the deal had not been finalized told The Associated Press that the two sides were close.
The Blazers need to strike a deal with Aldridge by Oct. 31 to prevent him from becoming a restricted free agent next summer.
Aldridge, the second overall pick in the 2006 draft out of Texas, was acquired by the Blazers in a draft-day trade from the Chicago Bulls. Last season, he averaged 18.1 points and 7.5 rebounds.
Mills fractured the fifth metatarsal in his right foot during practice in the offseason. It is not clear when he will return.
After starring for Australia in the Beijing Olympics and for Saint Mary's in college, Mills was selected by the Blazers with the 55th overall pick in the NBA draft.
The 6-foot, 175-pound Mills averaged career highs of 18.7 points, 4.0 assists, 2.6 rebounds and 2.5 steals during his sophomore season with the Gaels before deciding to turn pro.