(Bloomberg) -- Grifols SA's board of directors said it won't recommend that shareholders accept Brookfield Asset Management's indicative offer, which values the Spanish drugmaker at €6.45 billion ($6.8 billion).

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The offer "significantly undervalues the company's fundamental prospects and its long-term potential," Grifols said in a regulatory filing on Tuesday. The asset manager's disclosure was a tentative, non-binding indication requested by the Spanish regulator following media reports.

--With assistance from Jonathan Roeder and Catherine Larkin.