But Mylan CEO Heather Bresch told CNBC last month the deal was compelling for shareholders.
"I think there's going to be a lot of volatility in the health-care market for a while," Bresch said. "So I think as shareholders step back and say, 'It'd be better to be part of a larger base that could absorb that volatility,' ... I feel very confident we are going to get the tenders."
Papa said he estimates that 80 percent of his shareholders intend to vote against the deal, though he's still working to convince some hedge funds.
"We believe the right thing to do, as a standalone company, is look at continuing to grow our business by 5 to 10 percent organically, [and] supplement that with new products," Papa said. "We believe we'll launch over a billion dollars in new products over the next three years, and, of course, look at inorganic opportunities to supplement, just like we've done in the past. That, we think, is going to continue to generate more value for shareholders in the long term."
Shares of Perrigo were down 2.4 percent Monday afternoon, but are up about 2 percent over the past year. Shares of Mylan dipped 1 percent and have plunged more than 15 percent on the year.