The Portuguese was in flying form in the win over Manchester United on Saturday.
"I wouldn't say I'm already at that (pre-injury) level, I think I can do better," Pereira told reporters ahead of Thursday's clash with Spartak Moscow.
"That's what I work for every day. It was hard to have the injury, but it's in the past now and I have to do the best I can do and be stronger than ever.
"The team are very happy with the result and with the performance (against United), because we wanted to get back what we did in the past and show our quality. That was the game we needed.
"Now we need to keep going with this momentum, and that's what we'll try to do (on Wednesday), to play a good game and to get the three points.
"Especially having had two games with just a draw, it's important we don't wait until the last games. We need to start (on Wednesday), we can't wait any more."
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