Oxford United are eyeing a move for Sunderland defender Zak Johnson, with the club aiming to bolster their squad after relegation from the Championship. The 21-year-old spent last season on loan with York City and played a key role in their National League title success. However, Sunderland are expected to be prepared to let the centre-back leave this summer as he will struggle to break into the starting XI under Regis Le Bris. Johnson's contract is set to expire at the end of the month, and while he has been listed among the club's retained players, it is still likely he will move on. Oxford United and Wigan Athletic are currently showing the most interest in signing Johnson, with both clubs aiming to improve their squads for the upcoming season. The U's are looking to bounce back from relegation, while Wigan hope to build on a mid-table finish. York City are also keen to keep Johnson at the club, but they will face stiff competition from the two League One sides. Sunderland are planning ahead for next season after qualifying for the Europa League, with Le Bris hoping to improve his squad in a number of key positions. Johnson is not expected to play a part in the Black Cats' plans and will be allowed to leave the club. His likely availability as a free agent has placed a number of EFL sides on alert, with Oxford United and Wigan Athletic leading the chase. The transfer window is set to be an exciting one for Oxford United, with the club aiming to make a number of key signings to bolster their squad. Johnson would be a great addition to the U's, and fans will be hoping that the club can secure his signature. With the new season just around the corner, Oxford United are working hard to prepare for the upcoming campaign. The club's relegation from the Championship was a disappointment, but they are determined to bounce back and make a push for promotion. Signing players like Johnson would be a big step in the right direction, and fans will be eager to see who else the club can bring in. Oxford United's squad is taking shape, and the addition of Johnson would be a great boost. The club's management team are working hard to identify the right players to bring in, and Johnson is certainly one of them. With his contract set to expire, Johnson is likely to be available on a free transfer, which would be a great piece of business for the U's. The club's fans will be hoping that they can secure his signature and make a push for promotion next season.