The centre-back was forced off late in Friday's Nations League encounter, adding to Sunderland's concerns after striker Brian Brobbey suffered a similar injury while on international duty with the Netherlands.
Brobbey was substituted after just 35 minutes of the Netherlands' meeting with Germany on Thursday.
The Sunderland forward was seen clutching his leg while lying on the pitch before receiving treatment from medical staff.
Although Brobbey was able to leave the field under his own power, he was later seen limping heavily as he made his way towards the dressing room.
Netherlands coach Xavi subsequently confirmed that the striker had suffered an injury and would not continue with the national team.
“Brian is indeed injured, unfortunately, so we will call up another striker. We haven't decided who yet; I haven't had time for that yet,” Xavi told reporters.
Manchester United's Joshua Zirkzee was subsequently brought into the Netherlands squad as Brobbey's replacement.
Brobbey has since returned to Sunderland for further treatment.
The club then had another concern when Ballard appeared to suffer a hamstring problem of his own while representing Northern Ireland.
The defender's injury is particularly unwelcome for Sunderland given the importance of Ballard to their defence and the timing of the international break.
The exact extent of the problem is not yet known, and Sunderland will await further medical assessment before determining how long the 26-year-old could be unavailable.
The back-to-back injuries nevertheless provide an early concern for Sunderland, who will now hope both players can return quickly once the international break concludes.
Brobbey's injury had already forced the Netherlands to alter their plans, while Ballard's problem could leave Sunderland waiting anxiously for an update ahead of the return to Premier League action.