The Bulgarian has struggled for first-team football this season despite winning the Premier League's golden boot last term as the Red Devils were crowned champions
The Bulgarian finished as the Premier League's top scorer last season but has struggled for first-team football this term, making just 10 league appearances.
And the Red Devils boss conceded that, given his age, the 31-year-old may wish to leave in order to ensure playing time with opportunities limited at Old Trafford.
"His concern is not getting first-team football," said Ferguson. "At 31, he is looking at first-team football.
"It is difficult for me to guarantee that, so it could lead to him looking elsewhere.
"We will be taking up the option on his contract but, having had chats with him, I understand he wants to get first-team football.
"It is something we need to consider at the end of the season. For a player of his age and his ability, it is disappointing for him that he is not getting first-team football.
"We will look at the end of the season but until then, he remains at United."
The Scot also underlined the difficulty for the former Tottenham star in gaining a start ahead of in-form pair Danny Welbeck and Javier Hernandez.
He added: "He could play tomorrow [against Athletic Bilbao] but I have good options in terms of front players with Javier Hernandez, Danny Welbeck and Wayne Rooney."