Sergio Aguero will miss Manchester City's Premier League match against Cardiff City and is a doubt for Saturday's FA Cup semi-final against Brighton and Hove Albion.
Aguero was substituted before the hour during Saturday's 2-0 win over Fulham, having earlier dispatched his 29th goal of the season in all competitions.
Speaking at a pre-match news conference, Guardiola did not disclose the nature of Aguero's injury but he is not willing to risk the 30-year-old as City enter a pivotal phase of their battle for honours on all fronts – including the first leg of a Champions League quarter-final at Tottenham in seven days' time.
"He didn't train the last two days – tomorrow he is not able," the Catalan said ahead of a match where victory would see his team retake the lead at the top of the Premier League from Liverpool with six games remaining.
"Hopefully next Saturday, next Thursday but we will see the evolution of the next days.
"Him and Fabian Delph [are injured] and the other ones are quite well."
Aguero's absence means another chance to start for Gabriel Jesus.
The Brazil international threatened Aguero's status as City's number one forward after his arrival from Palmeiras in 2017 but is now unquestionably second choice.
Jesus has struggled to find his best form at times this term and only six of his 17 goals have come in the Premier League.
Nevertheless, Guardiola is satisfied with the 21-year-old's efforts.
"Of course. He made a good season," he said.
"It is not always easy to play at this club, as a striker in the position of Sergio.
"It's really not easy. Gabriel fights against a legend, an incredibly top player in the best season Sergio has had since we've been together.
"At the same time he's a respectful guy. When he played, he played well.
"Tomorrow he is going to help us, he is going to score goals and fight and create spaces for the other ones. He is going to do a good job."