Dustin Duncan's comments came after Premier Brad Wall posted the idea on Twitter on Thursday.
Wall's tweet came after he learned that a man in the province had been waiting more than three months for a test.
Duncan, who wouldn't identify the company that submitted a proposal, said the premier wasn't aware of the pitch when he made the comment online.
"We haven't yet had that conversation either at the caucus table or the cabinet table," Duncan said, adding that there is no draft legislation in play.
While there are private diagnostics companies in Saskatchewan, they are currently paid through the health-care system and do not receive payments directly from patients.
Duncan said allowing patients to pay for their MRI scans at private clinics would reduce wait times for diagnostic procedures and it would give individuals more health-care choices.
Saskatoon is the province's largest health region, and MRI wait times average 23 days for urgent cases, 93 days for semi-urgent cases and 140 days for non-urgent cases. The target wait time for an MRI scan in an urgent case is two to seven days.
"We have a lot of ... questions we need to answer before we make any type of decision, including what are the implications of going down this road," he said.
NDP Leader Cam Broten said privately paid diagnostics would lead Saskatchewan down the wrong path.
"The idea that a family or any individual who has the financial resources or the extra thousand dollars would be able to skip the line and get a surgery faster than someone who doesn't have the means to do that simply isn't right," he said.
"The answer is not to create this two-tier option where the rich can pay and where families who can't afford it are left in the cold."
Duncan said there would have to be a barrier between the public and private systems, so the private system wouldn't "poach" front- line staff.
"I certainly welcome an opportunity to have an adult conversation about the ability for patients to have choice," he said.
— By Clare Clancy in Regina