This season United achieved their highest Women's Super League points tally and secured qualification for the Champions League.

England striker Alessia Russo last week said she will leave United this summer.

A United statement read: "Everyone at the football club thanks Ona for her fine service and wishes her luck in the next stage of her career."

Batlle, the first Spaniard to play for United, is part of Spain's provisional Women's World Cup squad.

'United must act quickly' - analysis

Emma Sanders, BBC Sport

This is the second major departure from United this summer, but none will be more significant than Batlle.

She has proven her quality during her time at the club and is widely regarded as the best right-back in the world.

Barcelona's pursuit has gone on for a long time and they made enquiries last summer knowing Batlle only had a year remaining on her contract.

Similarly to Russo's exit, there have been frustrations over the slow efforts from United to tie down their best players with contracts nearing expiry.

Batlle needed to be playing Champions League football but, while United managed to qualify for next season's competition, the lure of returning to Spain and to join the recently crowned European champions was too big.

It could also have an impact on England international Lucy Bronze, who joined Barcelona last summer as their starting right-back.

United must act quickly to find replacements for Batlle and Russo, especially with the majority of the world's best players flying off to the World Cup in a few weeks.