Manchester United interim manager Ralf Rangnick wants his fullbacks getting forward as much as possible.

The German has players competing for both left-back and right-back positions heading into Friday's FA Cup fourth-round clash with Middlesbrough.

"They have to be defenders and, at the same time, give as much input as they possibly can if we're in possession of the ball," Rangnick said, during his pre-match press conference on Thursday afternoon.

"They should be offensive full-backs, offensive defenders. I think in the last couple of weeks, we have improved in those areas.

"It will also be an important position for tomorrow's game because Middlesbrough will play in a back five with very offensive wing-backs, at times even with five or six offensive players in the opposition's half.

"So, it'll be very important that we play tactically on a high level, with regard to our own full-backs."