Cal sophomore forward Ryan Anderson was also to remain in the draft and not return for his junior season, Anderson told ESPN.com Monday afternoon.
"I felt like this was the best possible decision for me," Anderson said. "Everybody kept telling me after my workouts that I'm an NBA player. This was, though, one of the hardest decisions I've ever made."
Italian star Danilo Gallinari will also stay in the draft, his father Vittorio Gallinari told 1050 ESPN New York's Andrew Marchand. Gallinari was considering dropping out of if he wasn't guaranteed a spot in the top 10.
The deadline to withdraw from the NBA draft was Monday at 5 p.m. ET.
Rivers, the director of basketball at Reebok, said that an MRI taken Monday on Walker didn't reveal a tear of the MCL or the ACL, which was feared when Walker heard a pop prior to working out for 21 teams at the Golden State Warriors' practice facility in Oakland.
Rivers said he is confident that Walker will be a first-round draft pick and that this latest setback wasn't enough to keep him out of the draft. Rivers said he was going to circulate the MRI results to teams over the coming days. He said there was an injury but he termed it a minor injury.
Walker has had multiple knee injuries during his playing career. He played in six games during the 2006-07 season before tearing his ACL in his left knee. He graduated from high school that October and became eligible for Kansas State in December. Playing as the understudy to Michael Beasley on the Wildcats this season, Walker averaged 16.1 points and 6.3 rebounds.
The 6-foot-10 Anderson, projected as a late first-round or high second-round pick, averaged 21.1 points and 9.9 rebounds a game for the Bears, who failed to secure a berth in the NCAA tournament last season.
Anderson worked out for Orlando, Toronto, Boston, Indiana, Detroit, Cleveland and Golden State, which was conducted at the Warriors' facility last weekend in front of 21 teams. He said he would sit down in the coming days to schedule at least six more workouts.
UCLA coach Ben Howland said Mbah a Moute will hire an agent and forgo his senior season with the Bruins. The 6-foot-8 forward from Cameroon became the first player to start in three consecutive Final Fours since 1999-01. He averaged 10.3 rebounds in the NCAA tournament, and had 12 points and 13 rebounds in UCLA's national semifinal loss to Memphis.
"After speaking to my family and going through the process, I feel like the time is right for me to take the next step in my basketball career and keep my name in the NBA draft," Mbah a Moute said in a statement.
Jordan, a 7-foot freshman center, told Aggies coach Mark Turgeon he would remain in the NBA draft with hopes of becoming the third Aggie taken in the first round since 2005.
Jordan averaged 7.9 points and a team-high 6.0 rebounds last season. The Aggies lost to UCLA in the second round of the NCAA tournament.
Texas A&M's Acie Law was taken 11th by Atlanta last year, and Antoine Wright went 15th to New Jersey in 2005.
Hendrix was the Crimson Tide's leading scorer and rebounder last season.
Information from ESPN.com senior writer Andy Katz and The Associated Press was used in this report.