Are only US employers eligible to participate in a QP?

[katieinny]

A business owner in the US owns a small company and maintains a 401(k) plan. He also owns a European company in which he is the only employee and sole shareholder. Other than the fact that the owner is a US citizen and lives in the US, there is no US presence for that company. He reports the income from the European company on his US 1040 tax return. Can the income from that business be included when determining his contribution to the plan? The accountant says that the income from the European business is reported as salary on his 1040.