The Boston Celtics have yet to land a true superstar in free agency or the trade market this summer, but it’s certainly not due to a lack of effort and team president Danny Ainge could even reinvigorate his previous pursuits for Los Angeles Clippers forward Blake Griffin or Oklahoma City Thunder point guard Russell Westbrook to achieve the team’s ultimate goal.

According to the Boston Herald, the Celtics “remain open to major moves” for such stars like Griffin or Westbrook, both of whom they’ve pursued before, but that no new talks have taken place. The report also stressed previous talks that would’ve shipped Chicago Bulls guard Jimmy Butler to Boston, and the signing of power forward Al Horford, might’ve been enough to sign Kevin Durant.

The Celtics pulled out all the stops in their attempt to lure Durant, even tabbing New England Patriots quarterback Tom Brady as a pitchman, but to no avail. Instead, Ainge didn’t completely whiff during free agency and stole Horford from the Atlanta Hawks for $113.3 million over four years.

However, while Horford’s one of the best two-way bigs in the league, Boston’s yet to land that true superstar like Griffin or Westbrook in free agency or by trade.

Landing any superstar comes with a unique set of problems, but Boston does have the requisite assets to at least tempt Oklahoma City or Los Angeles to answer the phone if Ainge calls in the near future.

The hurdles, in particular the asking price for Griffin or Westbrook, are significant. For one, both players will be unrestricted free agents in 2017, and the Celtics would require both players to sign contract extensions in order to consummate any deal. Otherwise Boston risks trading all of its most valuable young players and future draft picks with no assurance either player will stick around.

And right now, neither Griffin nor Westbrook might be open to giving up a chance to test the open market. Griffin’s scheduled to make $20.1 million next season and has a $21.3 million player option for the 2017-18 season, but the 27-year-old and five-time All-Star would likely opt-out in order to cash in on the NBA’s new ballooned salary cap. The same could also said of Westbrook, who has reportedly refused to sign an extension with Oklahoma City and intends to test free agency next summer.

Attaining Westbrook, though, does seem more plausible than Griffin at the moment. The Celtics have been labeled the frontrunner to land the former scoring champion Westbrook due to their considerable assets and that the Thunder are likely to move the All-Star “sooner rather than later.”

Griffin, on the other hand, has played a massive role in the Clippers rejuvenation from league laughingstock into perennial playoff contender since he was selected No. 1 overall in 2009. A highlight machine and former Slam Dunk contest champion, Griffin’s averaged 21.5 points, 9.6 rebounds, and 4.0 assists over his six-year career and he’s shown tremendous growth on the court under head coach Doc Rivers.

To put it another way, Griffin helped the Clippers win 32 games in his rookie season, 40 the next year, followed by a then franchise-best 56 in 2012-13. And since Rivers took over in 2013 the Clippers have won no less than 53 games each season, with Griffin the featured and primary scorer.

Rivers, who also serves as team president, even said after the Clippers were eliminated by the Portland Trail Blazers in the first-round of the playoffs that he had no intention of breaking up the core of Griffin, point guard Chris Paul, and center DeAndre Jordan. But the Clippers have plateaued these last two seasons and a shakeup may be necessary.

Trade speculation has continued to swirl around Griffin, who’s been linked to the New York Knicks and other teams before. And after a tendon injury and suspension for punching a team equipment manager limited him to only 35 games last season, the Clippers may decide to part with their most valuable asset.