It was about two minutes into the third period that Crosby slid into the offensive zone and stuck skating against skating with Chicago's Erik Gustafsson.
The Canadian dropped the balance, became semi-seated on the ice and was seen grimacing.
Crosby got up and went back to his own zone. There he blocked - with the same right foot he had just turned - a shot from Gustafsson.
The center star then went to change, went straight into the locker room and never came back to the match.
Coach Mike Sullivan didn't want to comment on the injury any more than he hopes to have more information after the team's training on Monday. Earlier, the team has lacked back star Kris Letang and Swedish forward Patric Hörnqvist.
The actual match? Chicago had the lead 2-0, but Pittsburgh took the game to an extension and then squeezed the extra point after penalty.
With Crosby gone, Pittsburgh's supporters were at least pleased that the team's other big star Jevgenij Malkin, who had just been away in eleven games with his own lower body injury, accounted for two assists.