Reports in Spain suggest the Premier League side will send the 22-year-old centre-back back to the Segunda Division in a loan deal with Girona
Reports in Spain claim the 22-year-old centre-back will be immediately loaned out to Girona, who have signed a number of City players on temporary deals in recent seasons.
"The club thanks Pablo Mari Villar for the commitment, discipline and hard work he has contributed during his three seasons with the first team," a statement on Gimnastic's website reads.
"Gimnastic de Tarragona wish him good luck on a personal and professional level with his new team, Manchester City."
Mari joined Gimnastic from Mallorca in 2013 and helped them to promotion to the Segunda Division in 2014-15.
The Tarragona-based club then followed that successful campaign up with a third-place finish in the second tier last season, losing out in the promotion play-offs.
Pablo Maffeo, Florian Lejeune and Ruben Sobrino are among the current and former City players to have been loaned to Girona, who also missed out on promotion to La Liga in the play-offs last term.