Nani, one of his team's major talents, was hurt during a 3-1 defeat against Turkey in a friendly game last Saturday. He sustained an injury to the same foot for his club Manchester United in January and missed two months of the season.
"Nani trained yesterday and tomorrow he will train again and then we will evaluate this injury that he had on the same part of the body as before," Bento told a news conference in Lviv ahead of the game on Saturday against Germany.
"We'll see after the training tomorrow how we proceed with him ... the only player we are not sure about is Nani."
The 25-year-old has played 54 games for Portugal, scoring 13 times.
Portugal conceded three bad goals against Turkey and the performance, combined with an earlier disappointing 0-0 home draw against Macedonia, prompted critics to speculate about whether the team is good enough to progress very far.
"I don't care about the criticisms because the people who deserve my attention are the players," said Bento.