Simmons, 27, had been a restricted free agent, but San Antonio has renounced his rights with hopes of signing him to a new contract. Thursday was the final day that teams could lift qualifying offers from restricted free agents.
Simmons' agent, Cervando Tejeda, says that his client is engaged in discussions with several teams around the league, and there's yet to be traction on a deal to return to the Spurs.
San Antonio also reached agreement on a guaranteed deal with Euroleague guard Brandon Paul, sources told ESPN. Paul, who played collegiately at Illinois, spent the 2016-17 season in Turkey and participated with the Cleveland Cavaliers in the 2017 Las Vegas Summer League.
Simmons blossomed over his two seasons with the Spurs. While his numbers during the 2016-17 regular season -- 6.2 points in 17.8 minutes per game -- were pedestrian, come the postseason, he showed he was ready for a more significant role.
In 15 games, the 6-foot-6 guard averaged 10.5 points in 20.4 minutes, notably helping the Spurs with MVP finalist Kawhi Leonard hurt.
Simmons went undrafted out of Houston. In 2013, he paid a $150 registration fee to join an open D-League tryout with about 60 players. His performance there eventually led to him to joining the Spurs' D-League affiliate in Austin, and he ultimately signed a three-year deal with San Antonio in 2015.
The Vertical first reported the Spurs' decision to renounce Simmons' contract.
ESPN's Michael C. Wright contributed to this report.