Messi, 35, will play his final game for Paris Saint-Germain this weekend, with his contract expiring at the end of June, and Xavi has not hidden his desire to bring the forward back to the Catalan club.
Xavi said recently he expects a decision from Messi next week, with a club in Saudi Arabia and Inter Miami also reported to be options.
Replacing captain Sergio Busquets, who will not renew his contract at the club, is another task facing Barca ahead of next season, with ESPN previously revealing Martin Zubimendi, Ruben Neves and Sofyan Amrabat have all been considered.
"[Messi] knows that and I have spoken with him. From there, Leo aside, the other priority is a midfielder [to replace Busquets] in the ideal scenario.
"I can't give names really, but the club know my priorities and also the targets. I have been very clear. There are names and positions are in place depending on different scenarios."
Asked if Barca were in a position to make Messi an offer financially, Xavi added: "That's the club's issue, it's a question for [director of football] Mateu [Alemany].
"I am not responsible for that side of things. On the sporting side of things, I think it would be a spectacular signing. He would help us a lot.
"I wouldn't say I am nervous [about the situation]. I am expectant because I have been speaking with [Messi]. I would be thrilled if he came back.
"However, it's more a decision for him to make right now, a personal one. I would understand any outcome, but as Barca fan I would really like him to come back."
Delaying Barca's ability to act decisively is their financial situation. The club have submitted a two-year viability plan to LaLiga -- which details how they will make cutbacks to be able to register new contracts and make signings -- and hope to have it approved soon.
Therefore, all deals are on ice, with Xavi also having to postpone making a decision on which players will be allowed to leave this summer until the financial position is clear.
"I have not spoken with anyone about leaving because maybe we can't even bring players in," he explained. "And, if we can't, I'm not going to speak with players about leaving.
"The situation doesn't allow me to act. We are on standby at the moment, waiting to find out the exact scenario and what we can do. We're dependent on LaLiga and this viability plan."
Barca are looking to build on the back of winning their first LaLiga title since 2019 in Xavi's first full season as coach.
Their campaign comes to an end on Sunday at Celta, who could still be relegated to the second division if they lose, and Xavi says Barca want to bow out with a win even though they have nothing to play for.
"We want to end the season well and we want to hit individual objectives, which are [Robert] Lewandowski winning the top scorer award and [Marc-Andre] Ter Stegen breaking the [LaLiga] clean sheet record," Xavi said.
"We don't have as much to play for as Celta, but we want to win. We've enjoyed this week, we have trained well and we will try to win."
Neither Busquets nor Jordi Alba will be involved in Vigo having played their final games for the club last weekend ahead of summer exits, while Ronald Araujo, Pedri and Alejandro Balde are all injured.
Youth team players Unai Hernandez, Marc Giui, Pau Prim and Dani Rodriguez will all travel with the first team to make up the numbers.