Chris Coleman believes continuity in selection has been a key factor in Sunderland's improved performances, but will not take any risks with John O'Shea this weekend.
O'Shea was substituted in the 70th minute during the 1-1 draw with Norwich City on Tuesday night, and the Black Cats boss believes his absence proved crucial.
He is unlikely to feature as Sunderland head to Reading on Saturday.
Coleman said: "John will struggle for Saturday, which is a great shame. He didn't train yesterday or today, he's been with the medical team and the physios.
"I analyse games all the time and had we had him on the pitch, just for his organisational skills, in the last five minutes against Norwich it might have been different.
"But his groin and his back were getting worse and worse and we didn't want to risk losing him for the rest of the season so we had to take him off.
"He's unlikely to be available on Saturday.
"He's one of those players where we keep thinking we'll have to give him a rest because he can't play Saturday-Tuesday at his age, but he does it all the time – he just gets through it when a lot of other players who are much younger have missed a lot more football.
"John doesn't even miss training, and maybe that's why he has played for as long as he has done, because of his attitude and his mentality."
Adam Matthews with also be missing due to a concussion, but Coleman is hoping for positive news on a key duo.
He said: "Adam suffered concussion after a collision in the first 10 or 15 minutes and was complaining of blurred vision at half-time.
"As soon as a player says that to the medical team, it is no longer a conversation – you have to put safety first so we made the change.
"Bryan had been out with a problem with his glute and then he got a knock in the first five minutes of the second half, but nevertheless he got through it.
"Paddy trained today, albeit under controlled circumstances, and was feeling good," Coleman added.
"He should train with us tomorrow, and hopefully he will get through that and be OK for Saturday.
"We are also expecting Marc Wilson to train with us tomorrow.
"If we have them both back, it will be very good.
"If you look at the make-up of the team [recently], there has been a certain type of physicality, pace, power, and we have been aggressive.
"We've had some good performances and of course that is helped when you don't have to make too many changes."
A negative result at the Madejski Stadium will leave Sunderland on the brink of relegation, with relegation rivals Bolton and Barnsley facing each other on Saturday fternoon.
Coleman says his team must keep themselves in the race.
He said: "Bolton are playing Barnsley this weekend so I look at what result would be best for us there, I look to see where Birmingham and Burton are, Reading too.
"There are all kinds of different scenarios.
"But what we have to do is make sure that come 5pm on Saturday, the other teams are still looking at where Sunderland are and they see us closing the gap.
"Two weeks ago, you would never have thought that Bolton would get sucked back into it.
"Birmingham are still in it.
"There's still a lot to be written yet, and the future is exciting because it is not written.
"At least we have a chance to write our own future, although of course it is going to take a big effort."