Rolen was taking grounders in the morning on a back field when a ball hit him on the fingernail.
"It ripped his nail completely off his finger," general manager J.P. Ricciardi said.
Rolen also broke the bone above the top knuckle on his right middle finger. It's unclear how long he will be out.
"It's a non-displaced fracture, which is the good news," Ricciardi said.
Rolen was acquired from St. Louis this offseason for fellow third baseman Troy Glaus in a swap of oft-injured All-Stars. Rolen was to travel to Baltimore on Sunday night to see Dr. Thomas Graham, the hand specialist who treated Toronto catcher Gregg Zaun's injured right thumb last season.
"He will see the specialist [Monday] and we will know more," Ricciardi said. "The fracture is actually not the problem. You can play with a fracture, it's just losing the nail."
Ricciardi is optimistic his new third baseman won't be out too long.
"I'm not a doctor, but the early prognosis is it isn't going to be six weeks, so I don't even want to throw a schedule out there. Our best-case scenario is that it's quick and our worst-case is it isn't as long as most things we have had to deal with. My instinct is I am preparing for the worst-case scenario but I can say this, he won't be lost for the year," Ricciardi said.
Marco Scutaro will fill in at third base while Rolen is out.
Blue Jays pitcher A.J. Burnett also has been hampered by a fingernail problem this spring. A broken nail on his index finger kept the right-hander him from throwing his curveball until Sunday, when he allowed seven runs and eight hits in 5 1/3 innings of Toronto's 15-7 loss to the Philadelphia Phillies.
"His curveball was rusty throwing it for the first time," catcher Rod Barajas said. "He made some mistakes but his stuff was there."
Phillies starter Cole Hamels gave up five runs and nine hits in 5 1/3 innings.
"It's not a lineup I would want to pitch against," Hamels said. "These guys are getting ready to go."
Scutaro hit a two-run homer for Toronto.