Ole Gunnar Solskjaer is wary of the threat hungry "old dog" Wayne Rooney poses to Manchester United's FA Cup hopes – and sees no reason why the club great could not be in the Old Trafford hotseat one day.

The Norwegian takes his side to Derby on Thursday night for a fifth-round tie that will pit them against a familiar face.

Rooney scored a club-record 253 goals across 559 appearances during a medal-laden time with United which lasted until 2017, when he returned to boyhood club Everton before embarking on a spell with Major League Soccer outfit DC United.

The 34-year-old returned to home soil to join Derby as player-coach at the end of last year and is now preparing to line up against his former club.

"He gave absolutely everything for this club and we all appreciate that," Solskjaer said.

"But any goal he scores against us will be chalked off his goal tally! He doesn't want to score too many of them.

"He's a threat – in and around the box, set-plays – and of course in this game Wayne will show what he can do and he wants to prove that there's still fight in an old dog.

"We've got to be on our toes, don't give him any space in and around the box or in midfield.

"At the latter end when he played in midfielder, you can see he's got Scholesy-like passing range."

Solskjaer praised Rooney's personality as well as his on-field performance ahead of clash with Derby, where his former team-mate is also working in a coaching capacity as he takes his first steps towards management.

The 34-year-old has made no secret about his desire to be the man in charge one day and Solskjaer was asked if Rooney could one day become United manager.

"Yeah," the current incumbent said with a laugh.

"It depends on how much you put into the job and how much you want it because it takes over your life.

"But it's the second best after playing, so I am sure there's many ex-players and managers around who would like to have my job."

Rooney has been away from United for several years but keeps in touch with some of the players and has even come into the dressing room after some games at Old Trafford.

"Hopefully he can come in and congratulate us after this game and wish us all the best after!" Solskjaer said before facing Derby.

"He's just such an infectious boy and he is just so positive and his aura... and he talks straight so he will give it to you if you need it."

Solskjaer, too, is a straight talker underneath his upbeat exterior, with the 'baby-faced assassin' ready to be ruthless in his bid to take United back to the top.

"Of course, I am (decisive)," he said. "I've got to make decisions and one day... well, you give them one warning and that's it probably.

"And then the next thing maybe they are not here anymore.

"You don't have to explain every time then. You might have to think about it after."

Asked how far this squad is from having the personality, drive and hunger he witnessed as a United player, Solskjaer said: "It is hard to say in percentages but we are getting there day by day.

"There's still some days here I am not 100 per cent happy with what's happened but you understand. We are human beings.

"They are disappointed – but get on with it.

"I am not going to feel sorry for you. You have to make yourself available for the next game and competitive situations.

"That is what I like and I like to see players who say, 'OK, he has left me out for two or three games without explanation'.

"I don't have to explain every time. Sometimes I do, yeah, but it's a way for me to say I need more."

And for those United players that do not react, it tells their manager everything he needs to know.

"Of course," Solskjaer said. "You can't just speak to them 100 times and say, 'now we need a change in you'. You've had opportunities."

United are set to be without Daniel James and Aaron Wan-Bissaka through knocks on Thursday, while Marcus Rashford remains out with a back injury and Paul Pogba has yet to return to full training after an ankle issue.

"Paul's still working with the physios outside," Solskjaer said.

"He won't be training with the first team until next week, so then let's see how long that will take. But he'll need some time to train, to get his football fitness back."