While Disney CEO Bob Iger likely considers Fox's entertainment assets crucial to catching online television company Netflix, Greenfield said Comcast CEO Brian Roberts needs a better foothold in international markets as the media industry reaches maturity in the United States.
"I think for Comcast there isn't an obvious fallback. If they want to create a global company like Comcast, I don't think there's a lot of other choices," Greenfield said Thursday on CNBC's "Squawk Box." "I think that's why, if you're Brian, you go all in to win and you simply do not lose."
"The U.S. media industry is slowing. Linear ratings are down, ... cord cutting is certainly growing, cord shaving is growing. What I think Comcast sees is: 'Look, the U.S. industry is slowing. How do we take advantage of what we do really well and replicate it all over the world where there's more growth potential?'" he added.
The analyst noted that Disney could consider a deal with companies like online music streaming platform Spotify or video game maker Activision to expand its media dominance should its bid for Fox fall short.
Greenfield spoke a day after Comcast announced a cash bid of $65 billion for the Fox units. Disney and Fox already agreed in December on a $52.4 billion all-stock deal for those assets.
Disclosure: NBC and CNBC are owned by Comcast's NBCUniversal unit.