"For me it's just a chance to get on the mound some more. Keep honing things in," Harrison said.
Harrison, who's recovering from spine surgery that he underwent a little more than one year ago, traveled with the club to Toronto so manager Jeff Banister and pitching coach Mike Maddux could get a closer look at the left-hander's throwing sessions.
As Harrison nears the end of his 30-day rehab period, Banister said the club is considering moving to a six-man rotation upon his return.
"I think there's a possibility of some form of it," Banister said. "I'm gonna go watch him throw his 'pen, and we'll continue to evaluate how he feels and where he's at, and also the structure of the rotation and how everyone else feels, too."
Harrison threw 104 pitches over six innings on Wednesday with Double-A Frisco.
• Injured outfielder Delino DeShields was having a workout day in Arlington on Friday and was scheduled to DH with Triple-A Round Rock on Saturday in Omaha. DeShields is on the 15-day disabled list with a left hamstring strain.
• Injured righty Ross Ohlendorf (right groin strain) was scheduled to begin his rehab assignment with Round Rock on Friday, while injured lefty Martin Perez (left elbow surgery rehab) was set to join Round Rock for his rehab assignment on Saturday.
Jamie Ross is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.