Varlamov took an errant shot to his neck area shortly after the teams took to the ice.
Islanders head coach Barry Trotz was not impressed to see his starting goalie go down at the hands of a teammate.
"To me, it's almost unacceptable," Trotz said, according to NHL.com's Dan Rosen. "To me, it's like running your quarterback over in warmup. Players got to recognize that your goaltender is almost your most important player on your team. You've got to get him warmed up. Guys are not thinking.
"It wasn't fair to Ilya, it wasn't fair to Varly, the way the guys warmed him up. It started in warmup and it just sort of carried over through the whole game."
Sorokin was drafted by the Islanders in the third round of the 2014 draft but didn't sign a contract with New York until last July.
The 25-year-old was long considered one of the best goaltenders outside the NHL. He posted a .935 save percentage in 40 games with CSKA Moscow in the KHL last season.
Sorokin's debut wasn't a success, as he allowed five goals on 32 shots in the Islanders' 5-0 loss.