Sources close to Zawaski have said that Toews suffered the concussion early in the Blackhawks' recent road trip. The source also implied that Toews may have hidden some of his symptoms in order to remain on the ice.
Toews will miss tomorrow night's game against the Dallas Stars with what head coach Joel Quenneville is calling an upper-body injury.
"He's progressing, but he's day to day," Quenneville said Wednesday.
This would be a major blow to a Blackhawks team that is starting to find its stride down the stretch of the season.
If Toews misses any significant time, the Blackhawks will have a hard time finding a replacement to fill the skates of Captain Serious.
Possible first line center replacements include Patrick Kane and Patrick Sharp, both of whom took face-offs in last night's game against the Detroit Red Wings.
The Blackhawks have won their last four games, two of them against Central Division opponents. Holding the number six spot in the West with 73 points, the Blackhawks need to make a push in their final 20 games this season in order to gain home ice in the playoffs.
Meanwhile, defenseman Niklas Hjalmarsson, who missed seven straight games with an upper-body injury, is scheduled to play Thursday against the Stars.