Alex Ferguson has admitted Manchester United old boy Carlos Tevez has already made his presence felt following his return to duty for Manchester City.
Ferguson branded Roberto Mancini's decision to recall Tevez after five months as an outcast an act of desperation.
After a slow start, Tevez has begun to repay the faith, scoring a hat-trick at Norwich a fortnight ago, a few days after opening his account for the season against West Brom.
Now Tevez is primed to face his former club, having already found the net three times in five previous games against them.
"He scored a hat-trick," Ferguson said. "That is an impact.
"We will just have to wait and see what he does on Monday."
Tevez's presence is just one of the sub-plots to what is generally acknowledged to be the biggest game of the entire Premier League season, which City go into three points adrift of United but with a significantly better goal difference.
Not that Ferguson is particularly relishing the prospect.
His side looked to have the championship sewn up when they led Everton by two goals with seven minutes remaining at Old Trafford on Sunday, only to "throw the game away", to use Ferguson's own words, as the sides played out a 4-4 draw.
It was the kind of self-inflicted wound United have endured so often during Ferguson's long reign. And it never gets any easier to take.
"I am a confirmed masochist," he said.
"I joined about 26 years ago. When the fixtures came out at the beginning of the season, it all pointed to this game. It was inevitable I suppose. In the context of our history, we almost expected it. Our supporters have been subjected to that drama for years and years. God knows what they are like just now."
It is true that United tend to make life hard for themselves.
The last-gasp 1999 Champions League final victory over Bayern Munich is the most obvious example, but there are plenty of other instances down the years where the Red Devils have staggered over the line after initially appearing to saunter towards it.
There is one clear advantage this time around, which could be vital: they do not actually have to win.
"We know the exact situation we are in here," Ferguson said. "We are in a better position than Manchester City.
"We can get two results, they can only get one. They have to win. We can draw or we can win, although you know my attitude and the club's attitude. We will be trying to win."
Ferguson reported no fresh injury concerns, meaning long-term absentees Nemanja Vidic, Darren Fletcher and Anderson will be the only ones who definitely miss out.