CHICAGO -- Bulls guard Lonzo Ball is expected to miss training camp and is doubtful for the start of the regular season because of lingering pain and discomfort following meniscus surgery on his left knee in January, sources told ESPN on Friday.

While a source reiterated that Ball's knee is structurally sound after he underwent arthroscopic surgery on Jan. 28, he continued to experience pain while attempting basketball activities as he spent the summer rehabbing in Los Angeles.

Ball will arrive in Chicago next week to undergo further evaluation by the team, but he is unlikely to participate when the Bulls begin training camp at the end of this month, sources said.

Throughout the summer, the Bulls have remained vague about a potential timeline for Ball's recovery while he has seen multiple knee specialists to determine the cause and treatments for the lingering pain and discomfort, sources said.

"He's getting better, probably not at the speed that we would like," Bulls vice president Arturas Karnisovas said in July during a broadcast for one of the team's summer league games. "But he's getting better."

When Ball suffered the initial injury in January, the Bulls announced an initial recovery timeline of six to eight weeks. However, Ball's knee never responded to several attempts by the team to ramp up his activity for a return to the court at the end of last season.

Ball was eventually ruled out for the rest of the season at the beginning of April, limited to a career-low 35 games. At his exit interview at the end of that month, Ball acknowledged that his knee recovery was "at a standstill."

Prior to the injury, Ball had been one of the sparks of the Bulls' fast start, averaging 13.0 points, 5.4 rebounds and 5.1 assists.

Chicago owned a record of 27-13 when Ball appeared in his last game on Jan. 14 before the Bulls finished 19-23 down the stretch without him and lost their first-round playoff series against the Milwaukee Bucks in five games.

Ball, who will turn 25 in October, had a procedure to repair a meniscus tear in the same knee in 2018 while playing for the Los Angeles Lakers, but he returned for the start of training camp then.