De Jong joined Barcelona from Ajax on a five-year contract in 2019 on a fixed annual salary worth £12m but he agreed to reduce his salary by £9.4m in 2020/21 and by £4.3m last season meaning he is owed £13.7m in basic wages.
He is also believed to be owed another £3.4m in waived bonuses for playing in at least 60 per cent of Barcelona’s matches over the previous two seasons.
De Jong extended his contract at the Nou Camp by a further two years to 2026, which allowed Barcelona to spread the deferred payments over a longer period.