George Baldock has signed a new two-year contract with MK Dons and agreed a season-long loan with Oxford United.
The defender made 12 appearances and scored one goal during a previous loan spell with the club last season before picking up an injury in April.
Baldock, 22, has made more than 50 appearances for the Dons, including in their 4-0 victory against Manchester United in the League Cup in August.
He has already joined up with the Oxford squad for pre-season training.
"I'm delighted to be under contract again with MK Dons," Baldock told BBC Radio Oxford.
"They made it quite clear earlier in the summer that they didn't want to let me go permanently, but they were happy for a season-long loan.
"It was then a no-brainer to join up with Oxford again."
Oxford manager Michael Appleton was equally pleased to see the return of the right-back, who has previously been on loan at Northampton, Tamworth and Icelandic side IBV, where he played in Europa League qualifying matches.
"There's no doubt George will strengthen our team and our squad," he said.
"He did ever so well with us last season and I think he will be a great addition.
"He will definitely be with us until January, but there are some recall clauses in there if MK Dons get injuries to defenders."
Meanwhile, Oxford United's longest-serving player, goalkeeper Ryan Clarke, looks to have played his final game for the club.
The 33-year-old is expected to leave the League Two side in a matter of days.
It follows the signing earlier this month from Scunthorpe of Sam Slocombe, who is expected to compete with Max Crocombe as first-choice goalkeeper.