Coach Randy Carlyle didn't know the severity of Bozak's injury. Bozak left the bench and went down the tunnel early in the second period, returned to play a handful of shifts and then did play in the third.
"When he went back out, he tried it. It wasn't able to go," Carlyle said. "That was probably about the 12-minute mark of the second period, so for half the game almost we were short. We had three centres. We're taxing a lot of people here right now."
When Bozak was in the game in the second, he had the primary assist on Phil Kessel's power-play goal that tied the score at 2. He took just three more shifts after that, including one that lasted only 13 seconds.
Bozak missed 12 games earlier this season with a hamstring injury. Going into Tuesday, he was among the NHL leaders in ice time for forwards.
The Leafs were already without centre Dave Bolland (severed tendon in ankle), winger Joffrey Lupul (groin) and defenceman Cody Franson (lower body).
This was the fifth straight loss for the Leafs, who have seen the injuries pile up.
"I think it's annoying for everyone," goaltender James Reimer said. "But at the same time, guys get opportunities. You've got to step in there and play well as a team. Last year we had lots of injuries, too, to key guys for long periods of time and we found ways to win. This season we've got to do the same thing and fight for each other."
Centre Nazem Kadri also missed the game against the Sharks because of a death in the family.
Follow Stephen Whyno on Twitter at @SWhyno.