As part of the marketing of the new Sega Genesis, Sega of America president and CEO Michael Katz planned to create a library of instantly-recognizable titles for the console by contracting with celebrities and athletes to produce games using their names and likenesses. As part of this, Sega signed a US$1.7 million five-year contract with Joe Montana, despite concerns among the Japanese executives that the game would not earn enough to cover this cost.
Since Sega of America did not at the time have a large game production facility and Sega of Japan had never designed a football game, Sega contracted with Mediagenic to develop the game for November 1989. No one at Sega was aware of the turmoil inside Mediagenic at the time; despite five months of reports that development was proceeding on schedule, Katz discovered in September or October that the game was hardly begun. To have a football game for Christmas release, Sega would have to find an already-completed game that could be converted.
Sega approached Electronic Arts, developer of the Madden NFL series, and president Trip Hawkins agreed to help. Joe Montana Football missed the Christmas deadline and was released in January 1991, shortly after the Genesis version of John Madden Football
Source: Wikipedia, "Joe Montana Football", available under the CC-BY-SA License.