A handful of recent top-20 NBA draft picks may be running out of time.

Some slow starters, like Mohamed Bamba and Markelle Fultz, are still young with room left to improve, so they'll have suitors lined up once they're available.

But the following five prospects could find themselves in trouble after the 2020-21 season. They've struggled to establish any one valuable skill, and a lack of evident improvement has created skepticism about their ability to break out.

Kevin Knox II, New York Knicks

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The revamped New York Knicks front office will need to take a hard look at Kevin Knox II during camp. Another season like last year will ruin his trade value, and if president Leon Rose is skeptical about his development, he may be better off shopping Knox now before teams stop buying his potential after three seasons of no improvement.

While most NBA sophomores' roles and production increase, Knox received fewer minutes and averaged 6.4 points for a 21-45 team. It's worth noting that he didn't have a long leash; David Fizdale was fighting for wins to keep his job (he didn't), and interim coach Mike Miller was also trying to prove himself.

But it's telling that neither coach had interest in involving Knox.

He isn't advanced enough with the ball to be used as a creator. Even with an advantageous mix of 6'7" size and athleticism for slashing, Knox has shown poor instincts and touch converting drives.

There was more hope that his value would show as an off-ball scorer, but Knox generated just 0.85 points per possession out of spot-ups (28th percentile) and 0.83 PPP off screens (29th percentile), struggling to consistently make catch-and-shoot jumpers, one-dribble pull-ups and line-drive takes to the basket.

For a non-playmaker, his inability to create or consistently make shots has made him unplayable at times, even if he did make strides on defense.

Though Knox just turned 21 in August, teams will start to forget about his age and worry more about his lack of progress if he's unable to make a third-year jump.

Maybe a new coaching staff will help Knox flip the switch. Perhaps he needs a change of scenery to a team that can offer a more defined role and supporting talent.

Or maybe former president Steve Mills and general manager Scott Merry totally misevaluated their 2018 lottery pick. There is no denying Knox's talent and skill set—the question is whether he will figure out how to apply and optimize them.

Dennis Smith Jr., New York Knicks

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Every offseason, it seems like hope is pumped into a Dennis Smith Jr. breakout projection. And every year, he's wound up looking worse than the one before.

Some have likely already written him off as a bust after he averaged 5.5 points and 2.9 assists in 34 games this year. It seems fair to conclude he won't come close to being the player who so many hyped out of high school and North Carolina State. But Smith is dangerously close to NBA rock-bottom and potentially needing to look for work overseas.

We'll give him one more season with good health and a new coaching staff, including Tom Thibodeau, who experienced years of success with scoring point guard Derrick Rose.