Nico was forced off early in the first-half after being clattered by Orient players.
Guardiola later said: “I think Nico got immediately what is the Premier League.
“I know without VAR it’s more difficult because they are not used to it and I know it’s a League One side, but there were one or two (missed) actions.
“There’s a penalty (that wasn’t given). I think Nico now understands perfectly what (English football) is.
“I don’t know how hard (the knock) is, but he could not continue.
“It was tough to finish the game with Rico and Bernardo at right-back and left-back, they are not giants like people I have seen at full-back.
“The first 10 minutes (Orient) attacked really good in the channel and then in the last 10 minutes - apart from that I think we played a really good game.”
Guardiola praised the competitiveness of Orient on the day.
“It was impossible to control (this game),” said Pep.
“In my nine years in England we’ve played many times against lower division teams in this incredible competition.
“The vibe, the crowd and everything. You play in FA Cup and you don’t find it in other places (countries).
“I remember Newport with Michael Flynn as manager, I remember Cheltenham and many others.
“Always we behave really good. We were lucky at the end because they create chances, but we created a lot, and their goalkeeper was really good.
“It was a tight game, but we knew it would be with the (style) that they have.
“We played with character, and we are in the next round and it’s always nice. In the last four or five years, we have been in semi-finals all the time.
“It’s good to continue.”