The manager reiterated his interest in bolstering his squad, but notes it could be hard to persuade players to make the switch halfway through a season
The reigning champions have experienced an indifferent season approaching the half-way point, as five losses in the Premier League have left them in seventh position, eight points off table-toppers Liverpool.
Moyes, however, has seen his side improve in recent matches following four straight wins in all competitions, with United topping their Champions League group and reaching the semi-finals of the Capital One Cup.
United's patchy league form had led to rumours the Scot could bolster his ranks, especially in midfield, but Moyes feels his targets are unlikely to leave their clubs midway through the campaign.
"We will look [at targets]," Moyes said. "But I wouldn't turn around and say that I'm massively sure that we will get them.
"Because a lot of the players we would be interested in wouldn't be available for us in that month of January.
"But we'll certainly be looking."
Man Utd struggled to sign players in the summer window too and only sealed the Marouane Fellaini on deadline day, with moves for Cesc Fabregas and Ander Herrera falling flat.