The show, hosted by Davina McCall, sees contestants gamble £1m on eight questions. If they get an answer wrong, they lose all of the money they bet on it.
According to The Mirror, producers are now checking one of the questions on Friday night's show.
McCall asked husband and wife Johnny and Dee to name the longest-serving Doctor on Doctor Who from a choice of Sylvester McCoy, Paul McGann, David Tennant, and Christopher Eccleston. The pair split their remaining £650,000 between McCoy and McGann but lost everything when McCall revealed that Tennant was the correct answer.
Tennant played the Doctor from 2005 to 2009, but some fans have complained that McCoy was the correct answer because he took on the role from 1987 to 1989 and in a 1996 film, with no-one else playing the Doctor in between.
Doctor Who Appreciation Society member Anthony Wainer said: "There are different ways to interpret it."
Meanwhile, a spokesperson for Channel 4 said: "The producers are investigating."