The Red Devils have been heavily linked with a move for Everton left-back Leighton Baines, while there have been reports of bids for Andres Iniesta, Miralem Pjanic and Marco Reus as the club look to bolster their midfield.
However, Moyes is adamant United would only make a move in January if they felt a player was right for the club and fit a certain profile.
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"We would like to but as always there is never any guarantee. If they’re [Everton] determined to hold on to [Baines] then he won’t be going anywhere and it’s worthless asking any questions."
Ryan Giggs turned 40 on Friday and Moyes had positive words for the Welshman. Asked where Giggs ranks in a list of Premier League greats, Moyes added: "Undoubtedly at the top because of his longevity.
"He’s played for one club, the amount of games, what he’s done in Europe, what he’s done in the Premier League. Every season you can look at Ryan Giggs moments.
"What he’s done is terrific, he’s an example to young players, how you should dedicate yourself throughout your career, and also to players in their mid-30s who think they’re coming to the end, but if you look after yourself and train well you can go on for longer."