But, having been named player of the year in his first season at the club, Valencia found the going much harder and decided to switch back to his old number, 25, for this campaign.
It seems to have paid off, with the Ecuadorean holding down the right wing spot under new manager David Moyes ahead of Wilfried Zaha.
In the Champions League win over Bayer Leverkusen last month he scored his first goal of the season, equalling his tally from the whole of 2012-13.
Robson is another former wearer of the number seven shirt, and he told manutd.com: "I just think Antonio has been very honest. Maybe he did feel a little bit of pressure when wearing the number seven.
"He won player of the year when he wore number 25 and, after an indifferent season for him, when he didn't always show the quality we know he's got, maybe there's a little bit of superstition to go back to the shirt he was wearing.
"So it's a good decision and a strong decision by him. I think he's started the season pretty well so that is good for the club and good for Antonio."
It has been a landmark week away from Old Trafford for Valencia, who helped Ecuador book their place at the World Cup finals in Brazil next summer.
A victory over Uruguay and narrow defeat by Chile were enough for Ecuador to pip the former on goal difference.
Valencia will now hope to end the week by helping United beat Southampton in the Premier League on Saturday.
The winger's decision means the number seven shirt is currently vacant, and Robson is hoping it will be taken by a marquee signing.
He said: "For me, if we can sign a player who is capable of wearing that number seven, like a David Beckham or Cristiano Ronaldo, then great. Hopefully, it could be Ronaldo again."
- Sports & Recreation
- Cristiano Ronaldo
- David Beckham
- David Moyes
- Eric Cantona