De Bruyne returned to the squad for the 3-1 win over Watford on Sunday but has not started a game since City's victory over Manchester United after testing positive for COVID-19 during the international break.
City have won five consecutive games in the Belgian's absence and Guardiola, who confirmed De Bruyne will start against RB Leipzig on Tuesday, insists the 30-year-old is aware of the task he faces.
"Kevin played all the season from the beginning, he arrived after the European Cup final in difficult conditions and then got corona[virus]," Guardiola told a news conference on Monday.
"He has to come back and fight for position. He does not have to show me anything. It's for himself; show what he's got and do what he's done for five or six years every three days.
"Competition is so necessary and he knows it but so does Bernardo [Silva] and all the wingers. They have to show it in five minutes or in 90 minutes, they have to show the quality for themselves and everyone.
"Kevin got corona[virus] when he was growing in his physical condition and it was a setback. The people who suffer feel so empty in the next days. Tomorrow he will start and we'll see how many minutes he can play."
City are on a run of seven straight wins in competitions and are already assured top spot in Group A of the Champions League before travelling to Germany to face RB Leipzig.
The game will be played behind closed doors after a surge of coronavirus cases in Europe and Guardiola has urged the public to keep following restrictions.
"The concern is because the situation is not good in Germany and we have to learn it's not solved," he said.
"Wear a mask, social distance and be careful. It would have been better to play with the people but if the authorities say behind closed doors you know it's because it's dangerous."
"They are 18 or 19-years-old and you have everything ahead of you," Guardiola said.
"The potential they have, fantastic young players, we all agree but they need to settle perfectly. The potential is there. if we have to use them it's not a problem."