The final chapter in a story which will be remembered for a long time by those who witnessed it, let alone those at the centre, came when Rooney signed a five-year contract extension with the Premier League club.
It commits Rooney to United until 2015 and makes him the highest-paid player in the club's history, with a new wage believed to be in the region of £150,000 a week.
The player had raised questions about United's ambition, with news he was looking for another club alerting Europe's big teams.
However, his U-turn prompted Gill to say: "It's a great day for the club. To those who say Manchester United cannot compete any more, we can - and we will continue to."
He added on Sky Sports News: "We are here to make sure we've got a great team and do what we do off the field by investing in the team and the facilities here.
"I fully understand that in order to have results off the pitch we need a great team on it.
"We've been challenging at the top of the table for years and intend being there for many years to come."
On Rooney, who is out for around three weeks with an ankle injury, Gill added: "By and large, everyone realises he is a great player.
"I'm convinced he'll get back to that form as soon as he's fit and back on the pitch."