The pair were both substituted after suffering injuries in Wednesday’s fractious Champions League clash with Atletico Madrid in the Spanish capital.
That game ended 0-0 but City progressed to the semi-finals with a 1-0 win on aggregate.
Both players were unable to participate as City held a training session at Millwall’s ground on Friday having travelled straight to London from Spain.
Guardiola confirmed playmaker De Bruyne had required stitches in a foot wound while Walker had suffered a twisted ankle.
Speaking at a press conference at the Championship club’s ground, Guardiola said: “They didn’t train today. We’ll see tomorrow but apparently it’d be so close after what happened on Wednesday.”
The ill-tempered affair with Atletico ended with a melee involving several players from both sides in injury time and further scuffles broke out in the tunnel afterwards.
Guardiola did not want to comment immediately after the match and was still in no mood to do so after two days’ reflection.
“It’s the past,” he said. “I’m not talking about it. We have an important game tomorrow.”
One player who was able to train on Friday was defender Ruben Dias, who was an unused substitute in midweek having been out since the start of March with a thigh injury.
Guardiola said: “He did train today. It was his third session with us.”
City are facing Liverpool for the second time in a week after last weekend’s thrilling 2-2 draw in the Premier League.
The result left Guardiola’s defending champions just one point ahead of their title rivals in the Premier League with seven games left.
Liverpool also progressed to the Champions League semi-finals this week with a 6-4 aggregate victory against Benfica.
The semi-final at Wembley will either end Liverpool’s bid for an unprecedented quadruple or extinguish City’s hopes of becoming only the second English team to win the prized treble of the Premier League, Champions League and FA Cup.