Sno was treated on the field with a defibrillator during the first half of NEC's match against Feyenoord.
The 25-year-old has a history of heart problems after suffering a cardiac arrest while playing for Ajax reserves in a training match in 2010.
The Hoops released a statement on their official website to give Sno their best wishes as he bids to recover.
A Celtic statement read: "The news that former Celtic midfielder Evander Sno had suffered a heart attack during a league game on Saturday was naturally a shock to everyone at the club and was quickly followed by an outpouring of concern for his well-being.
"Clearly all the best thoughts and best wishes of everyone at the Club are with Evander and his family at this time, and we are sure Evander can also count on the support from the entire Celtic family."
Sno spent three years at the Scottish champions from 2005, making 30 appearances during his time at Parkhead.