Oxford defender Liam Davis will have to go under the knife for a second time, the club have confirmed.
The 25-year-old was troubled by a groin injury throughout last season and had an operation at the end of the last campaign.
But U's boss Chris Wilder confirmed the left-back will need a second procedure and will miss the start of the season.
He told the club's official website: "Liam was struggling with this for much of last season and we booked him in to try and get it solved as soon as the season ended.
"Unfortunately that wasn't successful so he needs a second op.
"It's a shame for Liam but we are confident that this will clear the problem up and he will be back after the first month or so of the season."