Motiejunas, 28, last played in the NBA in 2017 for its New Orleans Pelicans. He’s spent the previous two seasons playing China.
Sanantonio (42-31) has lost two straight after winning nine in a row and it is now eighth in the Western Conference standings.
Motiejunas averaged 7.4 points and 3.8 rebounds per game in five seasons in the NBA, the first four of which he played with the Houston Rockets.
The Spurs will play Boston on Sunday, the second game of a three-game roadtrip.