The 19-year-old forward has had a particularly difficult time of it in the past 14 months, managing just five league appearances because of injury.
Fati missed the majority of the 2020-2021 season after tearing the internal meniscus of his left knee in November 2020, an injury that ultimately kept him out until September 2021.
But his return then was brief – he featured five times in LaLiga, scoring three goals, before then hurting his hamstring almost exactly a year to the day after suffering that initial knee injury.
Even during his short-lived return, Fati highlighted his importance to Barca – he averaged a goal every 71 minutes, the best record at the club this season (min. 200 minutes played) and was ruthlessly clinical, those three strikes coming from just 0.85 expected goals (xG).
Fati's xG over-performance of 2.15 is comfortably the best in the Barca team this season. Its current top scorer, Memphis Depay, has underperformance in relation to non-penalty xG (6.0 xG, five goals).
But despite the evidence showing just how much of an asset Fati can be, Xavi will resist the urge to play him against Granada in LaLiga on Sunday (AEDT), instead holding him back for a few extra days to feature in Thursday's (AEDT) Clasico in Riyadh.
"If it were the other way around, playing Madrid tomorrow and the Supercopa against Granada, I would do exactly the same," Xavi said.
"Ansu is fine, [but] I had some doubts that he would be able to play tomorrow's game. For now I prefer to wait because the last experience he had was a relapse.
"We love Ansu 100 per cent, and knowing that he is about to return is spectacular news for us. He has worked very well, with a very strong ambition, capable of making a difference.
"He is a fundamental player, but we do not want to take risks because we would lose him for the rest of the season. I prefer to wait until he is at full capacity – it's a question of physical condition."
Xavi was speaking a few hours after Philippe Coutinho's loan exit to Aston Villa was confirmed, a move that will go down well with many Barca supporters who had become increasingly frustrated by the Brazilian.
But while Coutinho may never have been the most popular player among fans, Xavi commended his attitude.
"It says a lot about him that he wanted to leave to have minutes," Xavi said. "His salary has been lowered. He is a great professional, who wants to succeed.
"Here he was struggling and he has looked for a solution. All the players are being very professional. I am delighted with those who play, but also with those who do not. They are exemplary."
Barca had been eager to move Coutinho on in part because of his massive salary, with the club needing to get players off the wage bill in order to register new additions.
Ferran Torres still cannot be registered after his move from Manchester City, though Xavi assured fans the club is doing everything it can to ensure the Spain international can play once he returns from his COVID-19-enforced absence.
"Today [Torres] has tested positive again. Regardless of whether we can register him or not, in principle he will not play [against Granada]," he continued.
"[Barca director] Mateu Alemany is working 24 hours a day so that Ferran can play when he tests negative for coronavirus. I am optimistic, I trust in the club management."