Sanchez, 30, arrived at the Copa America with his reputation in tatters after a miserable season with Manchester United in which he only scored two goals in all competitions as his side finished sixth in the Premier League.
The forward's struggles at United have been compounded by a run of injuries, including an ankle infection in May, and fans have been questioning the wisdom of shelling out a huge salary on the Chilean.
In Brazil, however, Sanchez has been able to lean on the support of his international team mates, with whom he won the last two editions of the Copa America.
"It's not easy to explain, but Alexis has come here and shown a lot of commitment and perhaps in Manchester he does not have the emotional bond he has with his team mates here, that affection," Rueda told a news conference.
"He's had bad fortune because Manchester United have had problems for a while, so he does not have the structure he has here. He has also had injuries, he's lacked consistency, he has lacked continuity."
Chile's all-time top scorer helped book his side's place in the quarter-finals of the competition by scoring the winner on Friday, finding the net with a smart half-volley early in the second half, having also scored in their 4-0 win over Japan.
"We have done brilliant work with him, we have given him a lot of warmth, which is what he needs. He has a special connection with the team and the group is very fond of him," added Rueda.
"He can recover because he is a natural born goalscorer but he has been anxious after the injuries, he looks after himself well and luckily has been able to rediscover his form."
Sanchez later said he had picked up an ankle injury in the first half but played on because he gives "everything for the national team".
"I have always had the enthusiasm to play but in England I've been given few opportunities lately," Sanchez said.
"But I'm relaxed, because representing your country is the most beautiful thing there is."
(Editing by Peter Rutherford)
