Bayer upped its bid on Thursday to $125 per share, from $122 per share.
Monsanto, the world's largest seed company, is open to doing business with Bayer or other companies, but called Bayer's bid "financially inadequate," Riggs said.
Monsanto might be considering a deal with another German company, BASF's (BASFY) agro-chem unit, Riggs said citing Bloomberg News.
If Bayer makes a higher bid Monsanto is in favor of, it would be the biggest German takeover ever, Riggs added.
Shares of Monsanto are up by 0.34% to $106.80 on Tuesday afternoon.
Separately, TheStreet Ratings team set this stock as a "buy" with a ratings score of B. The company's strengths can be seen in multiple areas, such as its good cash flow from operations and expanding profit margins. TheStreet Ratings team feel its strengths outweigh the fact that the company has had lackluster performance in the stock itself.
TheStreet Ratings objectively rated this stock according to its "risk-adjusted" total return prospect over a 12-month investment horizon. Not based on the news in any given day, the rating may differ from Jim Cramer's view or that of this articles's author.
You can view the full analysis from the report here: MON