His signing was, however, considered to have been quite the coup for United – with arch-rivals Manchester City having also expressed an interest – and Mourinho believes a proven performer will come good with a full pre-season under his belt.
He told ESPN: “It is not easy to come in the middle of the season.
“I’m not a big fan of the winter market because the players are coming in the middle of the season and it is not easy for them to adapt.
“So I think after a few months with us, now to start the season I think it is a perfect moment for him to establish himself as an important player for us.”
Sanchez has been a late addition to United’s squad kicking off the summer in America.
Visa issues prevented him from travelling with the rest of his team-mates, forcing him to initially work alone at the club’s Carrington training base.
He has, however, linked up with Mourinho’s side and played 65 minutes of a goalless draw with MLS outfit the San Jose Earthquakes on Sunday.
United are likely to call on him to provide attacking inspiration once again when they open their International Champions Cup campaign on Thursday.
The Red Devils are set to take on AC Milan in California before going on to face Liverpool and Real Madrid.
They will then return to Europe to take on Bundesliga champions Bayern Munich before starting the new Premier League season with a visit from Leicester City on August 10.