On March 3, 2019, Motiejūnas scored a career high 43 points, grabbed 17 rebounds, dished out 6 assists and led his team to a 122–83 victory. Despite a terrific 2018–19 CBA regular season, during which he averaged 27.3 points, 14 rebounds, 4.2 assists and 1.8 steals, his team was eliminated in the first round of the 2019 CBA Playoffs, after losing 113–105 to the Jiangsu Dragons on March 20, 2019.
On April 4, 2019, Motiejūnas signed with the San Antonio Spurs. He declined to sign a new contract with the Spurs because the Shanghai Sharks of the CBA offered a much more valuable deal.
On August 27, 2019, Motiejūnas signed a $6 million contract with the Shanghai Sharks (about $1 million per month). On October 1, 2019, he powerfully debuted his new team during a preseason game versus the Houston Rockets with 27 points, 11 rebounds, 3 steals and assists, however his team was crushed 71–140. On June 9, 2020, it was reported that Motiejūnas had parted ways with the Shanghai Sharks. In 28 games with the team, he averaged 22.8 points, a league-leading 15.1 rebounds, 3.5 assists, 1.8 steals and 0.5 blocks per game in 36.7 minutes of average playing time.