The Boston Celtics' coaching search remains focused in the ranks of assistants, with a wave of second interviews expected to come with Brooklyn's Ime Udoka, Milwaukee's Darvin Ham and the LA Clippers' Chauncey Billups, sources told ESPN.

Celtics president of basketball operations Brad Stevens, running the process to hire his successor, is trimming his list of candidates for the next phase of the process.

Udoka, Ham and Billups are among the prominent candidates left in the search, but aren't necessarily the full complement of the Celtics' remaining list.

Udoka has received strong reviews from Celtics players who played for the U.S. national team in the 2019 World Cup tournament, sources said. Udoka was an assistant under national coach Gregg Popovich. Udoka joined Steve Nash's staff this year after one season with the Sixers and seven years under Popovich with the Spurs.

Ham is considered one of the top head-coaching candidates among league assistants and has interviewed for several head-coaching jobs in the past two years. He has most recently been on Mike Budenholzer's staff with the Bucks and Atlanta Hawks, and broke into the NBA coaching ranks as a Lakers assistant in 2011. Ham spent eight seasons in the NBA as a player with six different teams.

In his first year as an assistant with the Clippers, Billups also recently interviewed for the Portland Trail Blazers' head-coaching job and has drawn interest from several more teams with openings, including Washington, Orlando and New Orleans, sources told ESPN.

Billups is a prominent candidate in the Blazers' search, sources said.

Billups was a five-time NBA All-Star in his 17 seasons as a player, including MVP of the 2004 NBA Finals with the Detroit Pistons.