Masayoshi Son has run almost all the way through ¥2.5 trillion ($23 billion) allocated to buy back SoftBank Group Corp. shares, raising concerns that his stock’s bull run will end without rapid intervention.

The Tokyo-based company purchased more than ¥2.1 trillion worth of its own shares over the past year through March, according to SoftBank filings, an unprecedented effort that more than doubled the value of the stock. Now, with only about 10% of the committed capital left, the program may run out as soon as next month, Bloomberg’s calculations show.

Already, there are signs the buybacks are losing their power to lift SoftBank’s stock. Shares declined 5.7% in March, their worst monthly performance since the pandemic-induced low a year earlier. They fell even as more money was spent on re-purchases, the overall markets advanced and SoftBank’s profit for the March quarter was expected to hit a record.