Lonnie Walker IV
Lonnie Walker arguably ranks as San Antonio's most talented player under the age of 25, however, he hasn't quite lived up to expectations yet. In theory, Walker could definitely be better than what he's shown in his first three seasons as a Spur. At 6'5" with a 6'10" wingspan, Lonnie has the size and length to be a great defensive player at his position. His eye-popping athleticism, shooting ability, and court vision should also make him difficult to guard on offense.
With Walker entering the fourth and final season of his rookie-scale contract, he has plenty of incentive to try and live up to his potential. He will likely serve as the Spurs' defacto sixth man next season following the departure of Patty Mills and should have plenty of opportunities to prove himself. Were Walker to have a great season, he can cash in once he becomes a restricted free agent. If that were the case, I believe his next contract could be in the range of 4 years, $50-66 million.
However, if his performance is underwhelming next season, he could be facing a tough restricted free-agent market (assuming the Spurs even extend him a qualifying offer). A few teams may show interest in him, however, they may be dissuaded from making an offer if they expect San Antonio to match. Additionally, it's unlikely that teams will value Walker enough to overpay him to the point that the Spurs won't match.
If he doesn't receive any significant offers, Lonnie might be forced to re-sign with San Antonio on a team-friendly deal. It would leave open the possibility that he eventually figures things out and plays well enough to exceed the value of his new contract. On the other hand, it would also give the team a potential trade piece if he's unable to improve.