Sanchez moved to Old Trafford from Arsenal in a high profile swap deal involving Henrikh Mkhitaryan moving to the opposite direction, but could not replicate his Gunners form at the Red Devils.
Sanchez was Manchester United’s highest earner on £400,000 a week but was shipped out on a season-long loan to Inter Milan last week.
"I think that I'm happy when I play for my national team," he told BBC Sport.
"I was happy at Manchester United too, but I've always said to my friends: I want to play.
"If they would let me play I'll do my best. Sometimes I'd play 60 minutes then I wouldn't play the next game - and I didn't know why."
Sanchez scored just five times in 45 games after moving to Old Trafford but the Chilean says he does not regret his decision to join Manchester United despite his ill-fated spell there.
"I'm very happy I went to Manchester United,” the former Barcelona forward added.
"I've always said that. It's the club that's won the most in England.
"When I went to Arsenal it was fantastic - I was happy there - but United were growing at the time, they were buying players to win something.
"I wanted to join them and win everything. I don't regret going there."
