Manchester City manager Pep Guardiola said his decision to leave John Stones on the bench against Crystal Palace was due to the defender's lack of match fitness.
Stones has not played for City since their 3-2 defeat by Norwich on September 14 and has featured just twice in the Premier League all season due to persistent thigh problems.
Guardiola's decision to start the match at Selhurst Park with Stones on the bench meant City's starting XI lacked a recognised centre-back, with Nicolas Otamendi out with a back problem and Aymeric Laporte still nursing a long-term knee injury.
"Nico [Otamendi] trained yesterday," Guardiola told Sky Sports. "He came back from international duty with a big kicking here training yesterday (gestures to back). I decided not to use him and John Stones has been away a long time and we have a game in three days so I decided to put Rodri in that position.
On Walker's absence, Guardiola explained: "He's sick. Has long problems with a stomach infection. He lost five or six kilos and he could not train in one day. He has not been fit since the last game against Wolves. In the second half he could not play and he is still not available.
"We have a lot of problems there (in defence) from the beginning [of the season] with Aymer [Laporte] out for a long time. John Stones as well. That is what it is, but I believe in the power of the team, I believe in the spirit.
"It's not the ideal situation but it never is in football. There are always some problems and we have to handle it."
