"We don't know, but it doesn't look good," Blue Jays manager John Gibbons said after Toronto's 10-3 win over Boston on Tuesday night.
Zaun exited the finale of the two-game set against the Red Sox in the second inning after he absorbed a foul ball off the bat of Boston first baseman (and former Blue Jay) Eric Hinske an inning earlier. Zaun was replaced by backup catcher Jason Phillips.
Zaun will visit a hand specialist in Baltimore on Wednesday, when the Blue Jays will determine whether they will place the 35-year-old on the 15- or 60-day DL. Zaun, who injured the area near his thumb on his throwing hand, will undergo an X-ray to evaulate the extent of the injury.
"We'll know more after we get the feedback from the hand specialist," Toronto general manager J.P. Ricciardi said. "Zaunie's a big part of our team. To lose him for any extended time isn't good."
Regardless of what type of DL stint is coming for Zaun, the Blue Jays plan on purchasing the contract of veteran catcher Sal Fasano from Triple-A Syracuse. Fasano, who signed a Minor League deal with the Jays this past winter, was hitting .297 with four home runs in 11 games for the Chiefs this year.
If Zaun is placed on the 60-day DL, that will clear a spot on the 40-man roster for Fasano. The Blue Jays will have to make an additional roster move to add Fasano if Zaun's injury only warrants a trip to the 15-day DL.
"The nice thing is we have Fasano to come up," Ricciardi said. "Between him and Phillips, we've got some veteran presence back there. On the positive side, Sal throws really well. So, if we start playing teams that run a little more, he helps us a little bit that way."
Zaun, who signed a two-year deal worth $7.25 million with Toronto in November, pulled himself out of Tuesday's contest. After catching one warmup throw from Jays ace Roy Halladay prior to the bottom of the second, Zaun tried to throw the ball back toward the mound, but it sailed into center field. He immediately walked back into the dugout and Phillips took over.
After Hinske fouled a pitch from Halladay off Zaun's hand in the opening frame, Zaun walked around home plate, shaking his right hand. Toronto head trainer George Poulis came onto the field to check with Zaun, but the catcher finished the inning.
For the season, Zaun is hitting .186 with one home run and eight RBIs in 20 games. The switch-hitter grounded out to shortstop in the second inning to drop to 2-for-15 at the plate on Toronto's current road trip. Zaun has managed just two hits since April 13.
Jordan Bastian is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.