2008-09: Lack appeared in 32 of 45 games for first-place Leksands in Sweden's Allsvenskan (second league). His 2.02 GAA was the league's second-best and he finished with a .930 save percentage and 4 shutouts. Leksands competed in the six-team playoffs to qualify for the Elitserien, finishing fourth with a record of 4-5-1. Lack played six of the ten playoff games and was 4-2 with a 2.36 GAA and .903 save percentage.
2009-10: Lack made his debut in Sweden's Elitserien as a 21-year-old and skated in 14 games as a backup to Florida Panthers' prospect Jacob Markstrom for Brynas. Lack had a 2.67 GAA and .911 save percentage as Brynas finished sixth in the 12-team league. Lack skated in two playoff games during Brynas' five-game first round series with Djurgardens and was 0-1 with a 1.53 GAA and .946 save percentage. In six games with Brynas' U20 team he had a 3.51 GAA and .884 save percentage. Lack signed a two-year, entry-level contract with Vancouver in April 2010.
2010-11: Lack appeared in 53 games for the Manitoba Moose and was named to the AHL's All-Rookie Team in his first pro season in North America. Lack was 28-25 with four of those losses coming in overtime and had 5 shutouts with a 2.26 GAA and .926 save percentage. Lack skated in 12 of 14 playoff games for the Moose and was 6-5 with 2 shutouts and a 1.99 GAA and .932 save percentage.
2011-12: In his second season in North America, Lack shared the goaltending duties for Vancouver AHL affiliate Chicago with free agent veteran signee Matt Climie. He was 21-23, with three losses in overtime, and had 4 shutouts in 46 games. Lack finished with a 2.31 goals against and .925 save percentage. The Wolves finished first in the Midwest Division and lost to San Antonio in overtime of the decisive fifth game in their first round series with the Rampage. Lack appeared in all five playoff games, starting four of them, and was 2-2 with a 2.17 goals against and .917 save percentage. He was re-signed by Vancouver to a two-year contract in August 2012.