Preston have made an offer for Oxford midfielder Ryan Ledson, Sky Sports News understands.
Sky sources have claimed the 20-year-old is potentially interested in a move to the Championship club this month.
But it is also understood Oxford are reluctant to sell the former Everton academy player, who has 18 months left on his current contract.
United boss Pep Clotet, who lost key players Marvin Johnson and John Lundstram in the summer, said last week: “I’m not thinking about players going out in the situation we’re in now.
“(Rumours) mean other clubs are interested in our players regularly. That means those clubs at a higher level see something that we’re doing right. They see a club with the right mentality which is developing young talent.
“(But) I have the same opinion I had on Thursday. It’s not about thinking about players going out, it’s about thinking about players coming in.”
Oxford landed highly-rated midfielder Cameron Brannagan in a permanent deal from Liverpool this week, while they have also signed centre-back Robert Dickie from Reading.