The Belgian midfielder, who joined from Everton for £27.5million on deadline day, was too far back in Sunday's derby loss to Manchester City according to Keown and the ex-Arsenal defender has implored Moyes to change that around.
"The derby was played at frenetic pace. Fellaini eventually got into it, but by then, the game was lost," Keown wrote in his column for Sportsmail.
"Moyes wants him deep in midfield but he must be played further forward. Fellaini was not effective at all in the final third because he hasn't got the legs to join the attack.
"People are watching United closely in that midfield area where Paul Scholes used to dictate the pace of games. Matches are often won and lost in midfield - and Yaya Toure was the clear winner on Sunday."