The Club's record goal-scorer returned to action against the Gunners having missed four months with a knee injury.
Now the City boss is hoping he can have a trouble-free campaign and get back to full fitness quickly.
"We are better with him on the pitch. It is good news he is back," said Pep.
"It’s important Sergio comes back in condition, starts to get rhythm, avoids injuries and plays good."
When asked whether the Argentine might stay beyond his tenth season, Pep said: "We know what he means to us. We appreciate it.
"Now he has to show, like everyone of us and me first, that we deserve to continue here, playing good and winning games.
"After that, the club and myself, we decide.
"But we don’t have any doubts about his quality. He is a player to stay until he decides because he is unique, with his numbers.
"He is important for our fans. It was four months out.
"Now he needs to start training and playing regularly and start to score goals. This is the most important thing."