Mashack was selected by the
Houston Rockets in the second round (59th overall) of the
2025 NBA draft, with his rights then traded to the
Memphis Grizzlies from the
Golden State Warriors via the
Phoenix Suns, in a deal exchange for the draft rights to the 56th pick (
Will Richard). He was the final selection in the draft. On November 16, the Grizzlies signed Mashack to a
two-way contract. He made his NBA debut on November 20 against the
Sacramento Kings, where he scored six points, and tallied up two rebounds in six minutes. On February 7, 2026, Mashack made his first career start against the
Portland Trail Blazers, where he totaled eight points, a career-high of six steals, one rebound, and one assist in 30 minutes, additionally, this was the first game where Mashack had to play the
center position due to the absence of players due to injury and the trade of
Jaren Jackson Jr. Mashack converted 3-of-9 field goal attempts and 2-of-7 three-point attempts. On February 9, Mashack scored a career-high 17 points against the
Golden State Warriors. On April 10, Mashack recorded a
triple-double with 13 points, 15 rebounds, and 14 assists in a 147–101 loss to the
Utah Jazz. The performance marked as a career-high in rebounds and assists for Mashack. Mashack finished the season averaging 6.2 points, 2.6 rebounds, and 2.2 assists. ==Player profile==