Oxford have announced that Plymouth striker Steven MacLean will remain on loan at United until the end of the season.
The 28-year-old's spell at the U's came to an end last Saturday but an agreement has been reached between the two clubs to extend the deal until May.
The former Scottish Under-21 international has so far scored twice in nine appearances for United since joining on an initial one-month loan in November.
MacLean told Oxford's official website: "I'm just happy it's all sorted out and I can now look forward to the rest of the season.
"Hopefully we can make a push for promotion, and with the players we have here, there's no reason why not."
United boss Chris Wilder added: "This is a fantastic boost for us. To sign a player of Steve's calibre shows the direction the club is moving both on and off the pitch."