Sanchez aggravated an old ankle injury in Friday’s 2-1 win over Ecuador that secured the reigning champions’ place in the quarter-finals.
If they avoid defeat against Uruguay at Rio de Janeiro’s Maracana stadium on Monday, they will win the group and play Peru in the last eight.
But a defeat would send them to a quarter-final against Colombia, who won a Group B containing Argentina with a 100 percent record.
“This is the theme to consider, as well as how he reacts today after training,” said Colombian Rueda.
“From what I’ve sensed, everyone wants to play tomorrow and everyone is very committed.”
Sanchez has started to rediscover his best form in Brazil following a dreadful club season with Manchester United.
He’s scored two goals in two Group C games — more than he managed in 20 Premier League matches for United this season.
“We can only decide (if he plays) after evening training, whether he can run, whether he can handle the workload,” added Rueda, who said that Sanchez would either start or not be involved at all.
Chile’s other main star — Barcelona midfielder Arturo Vidal — is also a doubt.
“Artur’s case also depends on how his muscle reacts to the recovery period,” said Rueda.
Monday’s clash promises to be a fiery affair as Chile and Uruguay have recent history.
In 2015, when Chile won the Copa America for the first time, they knocked out Uruguay in a controversial quarter-final.
Uruguay’s Edinson Cavani was sent off after picking up a second booing for flicking his hand into the face of Gonzalo Jara, in retaliation for the Chile defender trying to shove a finger up his backside.
Jara, who is unlikely to start the game, was also punched by Luis Suarez during a match in 2013 after touching the firebrand Uruguay forward’s testicles.
Rueda is more concerned about the threat posed by Uruguay’s talented strike pair than any potential trouble.
“Their great virtue is that they’re great finishers, they penetrate really well, they’ve scored an amazing number of international goals,” said Rueda.
Suarez with 58 and Cavani with 47 are the top two scorers in Uruguay’s history.