This is not a hypothetical nor a case-by-case situation.
The Red Devils simply must keep hold of their star playmaker.
The rumors on Rooney were strong earlier in the week, when The Daily Mirror's John Cross reported that the England international told teammates he wanted out of the club, and could be headed for Bayern Munich.
Those rumors were quickly compounded by a second story from The Daily Mirror which suggested that Chelsea could be making a move for the Red Devils' No. 10 , who, "had a plea for a move rejected by manager Alex Ferguson a fortnight ago".
That report goes on to state that contact between Rooney, United and Chelsea representatives has already been made, with Blues owner Roman Abramovich prepared to back any move by the Londoners. It also cites David Moyes' pending arrival as the new United manager (which hasn't been confirmed) as a possible sour point for Rooney, who doesn't have a strong relationship with the Everton boss.
United's response to these rumors and reports was simple.
"Wayne Rooney is not for sale," said a Manchester United spokesperson.
And whilst it's clear that United are happy with the 27-year-old's current performance, the rumors are certainly cause for concern at the Manchester club.
Rooney is a raw talent whose skills in the pressing game would be utilized even further under Moyes than they have been now. And given what we've seen from No. 10 throughout his time at United as both a striker up front and a playmaker in behind Robin van Persie, for him to get even better is a frightening prospect for the Red Devils.
Having Shinji Kagawa at the club offers them a great option in midfield, but the Japanese international doesn't offer them what Rooney can offer them in midfield—he can't provide them the same proven success with Robin van Persie and he doesn't have the same defensive game as the England star.
To sell Rooney now—once all the pieces have finally been put into place for United and once they've finally won back the league title—would just be madness.
United have made the right moves to remain firm on the Rooney despite the rumors, and as speculation for the summer transfer window continues to unfold, they must continue to refuse any offers for Rooney. As the 2012-13 season shows, he's simply too important to let leave—both now and in the future.
Rooney has two years left on his current deal at United.
At a minimum, the Red Devils need to ensure that he sees both of those out. It would simply be such a waste of he left under any other circumstances.
Hit me up on Twitter for more sports goodness: Follow @dantalintyre