With nearly $20 million in cap space and three trade exceptions, it's time for the Boston Celtics to stop saying “what if?” and start saying “who's next?” for the Kelly Green jersey—especially if they want to keep pace in what's becoming a frenetic race for a top-four seed in the East.

So who can GM Danny Ainge theoretically go and get to truly help his club? There are several guys that could be available, but only a select few who really make the most sense.

CELTICS' Cap Space, Picks and Trade Assets

2020-21 Cap Space/Remaining: $138 million hard-capped/$19.5 million

Picks Available: 2021-2025 firsts (own), 2021 2R: own and Thunder pick (if between No. 56 and No. 60); 2022 2R: own and Hornets pick (if between No. 56 and No. 60), 2025 2R: own and Grizzlies pick

Surprise Assets: $28.5 million trade exception, $5 million trade exception, $2.5 million trade exception

The Untradeable: PG Kemba Walker, SG Jaylen Brown, SF Jayson Tatum, PG Marcus Smart, C Robert Williams III

Intriguing Chips: SF Aaron Nesmith, PF Semi Ojeleye, PF Grant Williams, PG Tremont Waters, C Tacko Fall, SG Carsen Edwards, SG Romeo Langford, SG Javonte Green

Vets: PG Jeff Teague, PF Daniel Theis, C Tristan Thompson

Given the Celtics' situation and based on their assets and need, here are the two best trades they need to make before the trade deadline.

1. Harrison Barnes (Sacramento Kings)

Harrison Barnes, Celtics, Kings, NBA trade rumors

Currently in the second season of a frontloaded four-year, $85 million deal from Sacramento, the 28-year-old Harrison Barnes already has eight years of experience in the NBA. This 2020-21, he has played extremely well through their first 36 games, averaging 16.6 points, 6.2 rebounds and 3.5 assists on slashes of 49.4/37.0/82.5 with a 56.4 eFG percentage, which is all either at or well above career marks.

The 6-foot-8, 225-pounder has been particularly deadly from 2-point range, where he's shooting a career-best 56.9 percent. His overall shooting numbers are significantly higher than the league average.

Yeah, it has helped he's been alongside guys like De'Aaron Fox, Buddy Hield and rookie sensation Tyrese Haliburton, who've done nothing but successfully space the floor with speed and deep-shooting acumen.

However, if the Kings are hellbent on getting Haliburton more minutes as a future starter—while getting some extra cash/draft picks/rotation players—moving Barnes could be the way to do it. The back half of his contract is extremely franchise friendly, and the Celtics have been frequently mentioned as a team desperately in the mix for his services … as they should be.

The Celtics need another piece in order to help keep momentum rolling into the second half of the season. The Philadelphia 76ers, Brooklyn Nets, Milwaukee Bucks and Miami Heat are all currently above the Cs in the standings and riding the hottest streaks in the conference. The Atlanta Hawks are also scorching, as their five-game winning streak has moved them, for the time being, into the eighth seed.

Barnes seems like a natural fit to the Celtics roster, as well as in Brad Stevens' offense. He could be a second-unit forward behind elite wing Jayson Tatum if Daniel Theis and Tristan Thompson remained as starters, or he could slide in for Theis and create a massive four-out attack alongside Tatum, Jaylen Brown, Kemba Walker and some mix of Theis/Thompson/Robert Williams III at the five.

As they continue to struggle and fall behind in the West standings, “winning now” also doesn't seem to be in the cards for the Kings. Yet, Sam Amick of The Athletic brings a unique perspective owned by Sacramento.

For all the ink and airtime that has been spent discussing how Barnes would fit so well in Boston, or how other contenders might bring the 28-year-old forward their way, those sorts of scenarios obviously can’t unfold unless Sacramento is willing to send him out. So now, courtesy of a source with knowledge of the Kings’ plan, I present the other side of the Barnes situation: As it turns out, the Kings’ level of motivation on this front isn’t nearly as high as many may have believed.

In other words, Boston will have to make it beyond worthwhile to get it done. Is it worth the Kings' likely ransom? You bet.

2. Aaron Gordon (Orlando Magic) OR Thaddeus Young (Chicago Bulls)

Celtics, Aaron Gordon

Boston Globe's Chad Finn attests the Celtics don't need to make a major move despite owning the richest trade exception in NBA history (thanks, Gordon Hayward!), and he has some terrific points.

Brown and Tatum are All-Stars on exponentially incalculable trajectories, while Williams III is transforming into a two-way stud. GM Danny Ainge and his scouts have selected a young crop of talent with all of those horded picks, and the jury is still out on whether their impact is long term or not. The Celtics are also approaching the cap apron, so they could possibly want to remain south of the tax line.

However, Ainge has admitted that their 2020-21 roster, as it stands, is not championship ready. It's not a knock on the talent, per se, as it is more an indictment of a slow start and the excellent play of other Eastern Conference teams. Brooklyn, Milwaukee, Atlanta, Charlotte and Philadelphia also beefed up considerably either in the front office or in their rotations, leaving Boston with little choice but to upgrade at some point soon.

Both Aaron Gordon and Thaddeus Young find themselves in manageable contract situations and are strikingly similar offensively, with Gordon owning an edge in his 3-point shooting and Young nestling into a more defensive low-post role. Adding either player would keep the Celtics within the $19.5 million remaining against their 2020-21 hard cap, all while bolstering the forward position in different—but needed—ways.

The Bulls are still in contention for a playoff spot, while Orlando are near the bottom of the East. Dealing with the Magic, as opposed to dealing with the Bulls, might be a simpler situation and perhaps more fruitful with Gordon being younger (and, of course, a little more expensive) than Young.

Both players are also unrestricted free agents following the 2021-22 season, so if it didn't work, it's not like the experiment—or the price—would be so lofty.

Gordon's freak athleticism or Young's defensive savvy? Can't go wrong with either.