The likelihood of a potential competing offer by Comcast for Twenty-First Century Fox's movie studio and other assets has diminished, CNBC's David Faber reported Wednesday.

That's because Comcast, the parent of CNBC, is expected to raise its bid for Sky, the U.K. media company partly owned by Fox, which has recently boosted its own bid to acquire the remaining 61 percent stake it doesn't own. Comcast is expected to bid higher than Fox's most recent offer, Faber said on CNBC.

Fox shares fell nearly 4 percent Wednesday as the likelihood of a potential competing offer from Comcast for the movie and television assets "has probably gone down," Faber said. "How much is very much unclear."

Shares of Comcast rose 1.2 percent, while shares of Disney rose 1.8 percent.

Fox is refereeing a bidding war for its movie and television production assets between Disney and Comcast. Disney recently upped its bid to $71 billion in cash and stock, slipping above Comcast's $65 billion all-cash offer, which came last month in response to an earlier Disney all-stock offer.

The bidding for both Fox assets and Sky has pushed the potential value of those deals well above levels where they started out, Faber noted. The bidding for Sky is about 40 percent higher than where it started.