LONDON • Diogo Dalot has not had much of an opportunity to impress the Old Trafford faithful, having arrived in the summer injured.

But the Portuguese teenager, who finally made his Manchester United debut against Young Boys in the Champions League last Wednesday, did enough in Switzerland to warrant a starting place against Derby in the third round of the League Cup today.

"He plays on Tuesday again. I want him to play totally fresh. To play for Manchester United is difficult enough for a kid of 19 coming from another country and after an important (knee) injury and surgery," United manager Jose Mourinho said of his £19 million (S$33.9 million) full-back ahead of his side's home tie with the sixth-placed Championship side.

"He is a player to be here for competition for positions. He's a very good player."

There will also be a reunion of sorts for Mourinho and new Derby boss Frank Lampard, who was one of the Portuguese manager's trusted lieutenants on the pitch during a trophy-laden spell at Chelsea, winning two Premier League titles, one FA Cup and two League Cup trophies together from 2004-07.

And the former England midfielder revealed that the pair had spoken ahead of Derby's visit to Manchester.

While the Red Devils have endured an indifferent start to the campaign, Lampard is aware his side still have their work cut out for them.

"We've spoken in the last 24 hours, it was very brief but we talked (about) family. I learnt a lot from him and I appreciate it," he said.

"We (Derby) know what we're coming up against. A great Manchester United team that's been put together. Whether we can win or not is a very tough order, but we need to have our fans coming away proud of the team."

Besides Dalot coming into the team, Mourinho is also expected to ring the changes, with Anthony Martial, Juan Mata and Scott McTominay potentially featuring, while Nemanja Matic could also make an appearance after serving a one-match ban over the weekend.

Cross-town rivals Manchester City kick off their League Cup defence, with the Premier League champions travelling to Kassam Stadium to take on third-tier Oxford United today.

With Oxford languishing second from bottom in League One, Karl Robinson's men are not likely to put up much of a challenge to City, even though manager Pep Guardiola confirmed that he would be giving some of his fringe players a run-out in the third-round tie.