Valencia made 43 appearances for the Red Devils last season as United won the Europa League and the League Cup.
Anthony Martial and Marcus Rashford's fierce competition for a starting place in the match-day XI has both players finding new levels.
English Premier League club chiefs are gathering in London today for what is being touted in some quarters as one of the most important meetings since the league's creation in 1992.
This is the Manchester United that has been missing at Old Trafford.
Matic added: "We cannot be relaxed for the future because we have to win more, focus because the teams now know how we play, the teams know our formation, our players and, of course, in the future those will want to show they can play against Manchester United".
Trump Rips San Juan Mayor: 'Told by the Democrats to Be Nasty'
President Donald Trump says Washington is - in his words - "fully engaged in the disaster and the response and recovery effort". Cruz also said she and her family are staying at the Coliseum in San Juan , along with more than 600 people.
Crystal Palace, which has yet to garner a point, is at the bottom of the table. And with the lone loss to Real Madrid as the only blemish on the season so far, I don't think any of the Old Trafford faithful can find room to complain.
So when speaking with local journalists this Monday, Mourinho was asked about the matches against the Eagles, but still claimed they will be the toughest opponents in the group. They also have the form of Marouane Fellaini - once booed by United fans - to be thankful for. After the October worldwide break, Manchester United will have to show what they can do against challenging teams.
The issue has been simmering for years and former Liverpool CEO Ian Ayre has led calls for clubs to be able to sell their foreign rights on an individual basis which would allow the big ones to cash in more on their global marketability.
Fans can bring their official club shirt to be printed with a Premier League player's name - for free.
The Foxes failed to earn their first win since a 2-0 victory over Brighton and Hove Albion on August 26; they are now in 17th place with just five points.
In short then, United have looked exceptionally good in games they struggled in last season, but it's too early to tell if they are really the title challengers Mourinho needs them to be.