Detroit Lions assistant Curtis Modkins, whose responsibilities consisted of coordinating the run game, could be joining Chip Kelly’s staff with the 49ers.

Modkins has emerged as a “key candidate” to become Chip Kelly’s offensive coordinator, reported the NFL Network’s Ian Rapoport.

[MAIOCCO: 49ers fire offensive coordinator Chryst, nine others]

Ryan Day, a three-year starting quarterback for Kelly at New Hampshire and his quarterbacks coach with the Philadelphia Eagles, has already joined the 49ers’ staff, a source told CSNBayArea.com. Day was originally reported to be the top candidate for offensive coordinator, according to ESPN. But it appears Day could be back on Kelly’s staff in the same role he held with the Eagles.

Kelly, as he has done in the past, is expected to handle the 49ers’ play-calling.

[MAIOCCO: Preview of Chip Kelly's first 49ers press conference]

Modkins, 45, served as Jim Caldwell’s run-game coordinator and running backs coach since joining the Lions in 2013. The Lions ranked third in the NFL in 2013 in total yards gained by running backs with 2,769 yards. But the Lions ranked last in the NFL in rushing yards last season at 83.4 yards per game.

Modkins was offensive coordinator/running backs coach for the Buffalo Bills from 2010-12. The Bills ranked fourth in rushing average (5.0) and sixth in rushing yards (2,217) in his final season on Chan Gailey’s staff.