Ole Gunnar Solskjaer quipped that any goals "old dog" Wayne Rooney scores for Derby County against Manchester United on Thursday will be chalked off his record tally.
Rooney is set to captain Derby against his former club in an FA Cup fifth-round tie at Pride Park.
The former England captain scored a record 253 goals in 559 games for United before returning to Everton in 2017 and joined the Rams as a player-coach in January after a spell in MLS with DC United.
Solskjaer knows his side must be wary of his former team-mate Rooney, who is his son Noah's favourite player, and joked the 34-year-old should have a good reason to avoid finding the back of the net.
The United manager told a press conference: "He gave absolutely everything for this club and we all appreciate what he's done, but any goal he scores against us will be chalked off his goal tally, so he doesn't want to score too many.
"Wayne will show what he can do, he wants to prove there is 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, because you can see his Scholesy-like passing range."
Solskjaer went on to dismiss any suggestion that Rooney's contribution to United's cause has been undervalued, adding: "He's been a fantastic player for Man United. And he played here for so long. He's the club's top scorer, he won so many trophies.
"For me, I don't think the fans underrate him, I think everyone really, really appreciates what he did for us, he's still very welcome, he's still around the place, he still comes to Old Trafford, so he will get a good reception from our away fans in that game."
The Norwegian head coach added on Rooney's ambitions to move into management himself when he finally hangs up his boots: "I think he just wants to stay in the game, as many of us do, and he's a great person, he makes everyone feel good – whether you are 80 or 10.
"He's even my Noah's favourite player, not just because what he did as a player, but the kind of human being he was in and around the place.
"I'm sure when he becomes a manager he'll affect his players. When he's coaching, he's so enthusiastic about the game and he knows the game."