Walker has been sidelined with an ankle knock since our quarter-final second leg tie away at Atletico Madrid earlier this month.
Stones meanwhile, missed last Saturday’s Premier League win against Watford after having come off reporting muscle tightness during our 3-0 win against Brighton last week.
Meanwhile, Joao Cancelo will definitely miss the game through suspension.
Addressing the media on Monday ahead of the visit of the La Liga leaders, the City manager said he would carefully monitor Stones and Walker along with the rest of the squad at training before making a final decision.
But he acknowledged there were concerns over if the pair would recover in time.
“They are doubts, they didn't train for the last week, ten days, John since Brighton. We will see how they feel, and take a decision tomorrow,” Guardiola revealed.
“We have a training session this afternoon at 4. We will see how they feel.
“We have time tonight and tomorrow morning to decide. I have to see today's session to decide.”
Tuesday’s tie brings City back face to face against the most successful side in European history with Real having lifted the famous trophy 13 times while we reached the final for the first-time last season.
The pair also met in the semi-final back in 2016 when the Spaniards won 1-0 on aggregate but City avenged that loss with a last-16 triumph in 2020.
Looking ahead to a game which has captured the attention of Europe, the boss described it as another opportunity for City to write a memorable new chapter in our history.
And, despite the pressure and what is at stake, the boss also urged his players to relish and enjoy the occasion.
“It’s an honour to be here in the semi-final playing Real Madrid. In the last decade we start to be there and it’s an honour to be here. We try to do a good game,” Guardiola added.
“If we had to compete with history, we wouldn't have a chance. Their history speaks for itself.
“We have to have the desire to compete against them. To play against Real Madrid is an incredible test. We want to try it. We need to suffer, to stick together, when we have the ball try to attack.
“It would be the same if we face Bayern Munich or Barcelona, the teams who have been here many times. A decade ago we weren't here and now we are here. It’s good lessons for the future.
“The history, we cannot change it. Tomorrow, we play 11 v 11 and the players will decide if decision making is good.
“We play against players who have been in this position many times. That's why they have things that maybe still we don't have. But maybe there are things we have they don’t have, I don't know.
“At the end it is 11 v 11, they have quality and it’s how strong they are mentally.
"This game will not be won by me or Carlo (Real boss Ancelotti) - it’s the players.
“Being in the semi-final is so good. One day we will not be here because it’s so demanding – look at the big teams who are not here.
“I say to the players, enjoy that moment. You never know if we will be back here at any stage.
“We try to be ourselves in the good moments and bad moments.”