Xabi returns La Real for the first time since leaving the B team coaching job for Bayer Leverkusen.
He said at today's media preview: "This isn't my first big test. Each match is very important, and the points can be decisive in the long run."
Asked if his father will support him or Real Sociedad, Xabi smiled: "You'd have to ask him, but I hope it's with us."
On the form of Kylian Mbappe, he continued: "Kylian is in good shape, not just physically but also personally. He embraces that role and that shared responsibility.
"Rodrygo and Vinicius can play, it's not something that's ruled out even though we haven't done so yet. We need to remain calm and have ample time.
"We're in a phase of assimilating everything. We need more blocks and more games. We want to change things up, and we're physically better. We need fresh players who feel like they can participate at any moment."
Xabi also raised the prospect of Jude Bellingham returning early after his shoulder operation.
He said, "I want to be optimistic and hope he's ready before October. He's done partial things with the group, but we're protecting him. He's made a great effort, although he won't be back tomorrow. We're waiting for him."
Xabi was also asked about the competition between right-backs Dani Carvajal and Trent Alexander-Arnold, with the club captain favoured by the coach in the opening games of the season.
He added, "Competition is healthy, and that's important in the locker room. Not just at full-back, but in other positions as well. Whoever deserves to play, will play."