Wedbush said it saw the potential for an improved offer after Sanofi publicized a non-binding proposal to buy the prostate cancer treatment developer for US$52.5 a share in cash.
The broker's David Nierengarten said: "We believe Medivation could be worth US$55 to US$63 per share in an acquisition based on operational synergies."
Sanofi said earlier Thursday that it believed combining the two companies represented "a compelling strategic and financial opportunity to drive significant value for the respective companies' shareholders, employees, patients and caregivers."
Sanofi chief executive Olivier Brandicourt said: "Last November, Sanofi outlined our mid-term strategy which includes rebuilding our position in oncology, one of the largest and fastest growing therapeutic areas in the biopharmaceutical sector.
"With Medivation's best-in-class offerings in prostate cancer, we believe a combination would benefit patients and, at the same time, generate value for shareholders of both companies."
Drug majors are increasingly seeing acquisitions as a way to boost their new product line-ups as patents on existing treatments expire, attracting copycat competition.
Sanofi itself acknowledged the speculation that it could bid for Medivation, saying its proposed offer price represented a premium of more than 50% to Medivation's two-month volume weighted average price "prior to there being takeover rumors."
Credit Suisse said in a note last month that Medivation, which has a market capitalisation of about US$9.26bn, could be worth up to US$75 a share.