Sources: Portland Trail Blazers' Damian Lillard off-limits in trade talks for Philadelphia 76ers'...

As the Philadelphia 76ers begin to gather momentum in trade conversations for All-Star guard Ben Simmons, the Portland Trail Blazers reiterated that one of the Sixers' top targets -- All-NBA guard Damian Lillard -- is not available to be discussed, sources told ESPN.

The Sixers and Blazers connected in recent days and Portland interim general manager Joe Cronin made clear to Philadelphia that the franchise still plans to continue building around Lillard, sources said.

Nevertheless, the Sixers are becoming more engaged on multiple fronts in talks centered on Simmons. Philadelphia has been aggressively trying to assemble two- and three-team deal structures to land a package that would include a top 25-level player, sources said.

Much of the increased momentum centers on Wednesday, when many players signed in the offseason as free agents become eligible to be traded. Starting Dec. 15, 84% of the 446 players under contract can be included in deals. Currently, 65% of the league's players are eligible.

The Sixers have long targeted Lillard, who reaffirmed his desire to stay in Portland around the start of the team's training camp. After the recent firing of president of basketball operations Neil Olshey, Cronin has publicly and privately said the franchise plans to keep building around Lillard. The Blazers have been open to discussing a deal for Simmons centered on guard CJ McCollum, but that conversation never gathered traction, sources said.

Simmons has yet to play for Philadelphia this season, saying he was addressing his mental health before rejoining the team. He made a trade request after the Sixers' loss to Atlantain the Eastern Conference semifinals last season.

ESPN's Bobby Marks contributed to this report.