The 27-year-old, whose future at Old Trafford was the subject of speculation over the summer, struck twice in midweek against Bayern Leverkusen after netting against Crystal Palace
The England international became just the fourth player in United's history to reach the 200-goal milestone for the club thanks to a double against the Bundesliga outfit on Tuesday night.
Wayne Rooney is 15/2 with bet365 to open the scoring against Manchester City
"He's worked hard and is showing exactly what he can do," the Scottish manager told reporters.
"If Wayne could score another two goals at the weekend that would be the next step forward. I'm asking him to step up again."
The Scot also confirmed that the derby is just as important to players as it is to the fans, and appreciates that the points could be crucial as two of the major title contenders go head-to-head.
"There is an excitement for any derbies in any big city in the world. They're all really important to your own supporters," he added.
"They're important to the players as well but ultimately it's about what happens come the end of the season and how many points you get together to see who is top.
"These points could be really important towards that, they may not be. We'll go and we'll try and take all the points."