Playmaker Rosicky missed the Czech's final Group A game against Poland, returning to Prague for treatment before rejoining the squad.
"After training the chance of me starting tomorrow is bigger," Rosicky told a news conference at the National Stadium.
"I have trained today but we will have to see tomorrow if I am able to play. We will decide on how the injury reacts."
The midfielder has been having intensive treatment since injuring his foot in the second group match against Greece. He was replaced by Daniel Kolar in the creative role behind Milan Baros.
Rosicky, sporting a beard along with the rest of the Czech squad, said he and his team mates would continue to grow their facial hair for as long as they remained at the tournament.
"We look scary as a team. Hopefully they (the beards) will get worse and worse," he joked.
Rosicky was also in light-hearted mood when asked, as a Premier League player with Arsenal, to list the attributes of Portugal dangerman and the world's most expensive player Cristiano Ronaldo, once of Manchester United.
"He does not want to defend," Rosicky quipped. "But he can afford not to help his defence because of his quality and the level he plays at."
Czech coach Michal Bilek said his side, who rebounded from an opening 4- 1 defeat by Russia to beat Greece and Poland to go through to the last eight as group winners, would again adopt the more defensive tactics that served them well.
"Portugal are a very compact, well-balanced side," he said. "Ronaldo is dangerous but he is not their only dangerous player. You have Nani, Postiga...
"Against Russia we opened the game too much and they punished us. We strengthened the defence and that has been the key. We have learned a lot from our first match."
The Czechs - the only team to reach the last eight with a negative goal difference - will ask defender Theodor Gebre Selassie to mark Ronaldo, who shone for the first time in the tournament when he scored twice in Portugal's 2-1 victory over the Netherlands on Sunday.
Bilek said it would be an "interesting challenge" for Gebre Selassie.
"Ronaldo can score 40-50 goals in a season," said the coach. "But it's not just up to Theo, we all have to defend well. If he runs it is impossible to stop him."