Rooney has missed the entirety of United's pre-season campaign due to a series of injury problems, but featured for his country on Wednesday as they beat Scotland 3-2 at Wembley.
And Welbeck, who also started for Roy Hodgson's side in the friendly encounter, has revealed his happiness at being able to link up with Rooney again.
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"Once we're on the pitch we know each others' games. I'm just really happy for him to get out on the pitch and get his first game of the season.
"We all know the quality Wayne Rooney possesses. To have him on the pitch for Manchester United is a bonus."
Rooney's future has been shrouded by doubt throughout the close-season after the striker handed in a transfer request upon the conclusion of the 2012-13 campaign.
Having already rejected two bids from Chelsea for the former Everton striker, new United manager David Moyes has repeatedly insisted Rooney is not for sale.