The 24-year-old sustained the injury before Sunday's 1-0 victory over rivals PSV, a seventh Eredivisie win in a row that keeps Frank de Boer's side top of the table.
De Jong has only made 10 league appearances this season as his campaign has been blighted by injuries, but the prognosis for the current problem was better than expected.
"An MRI scan no serious damage was found Monday," a statement read on the club's official website.
"The diagnosis is that the muscle is slightly strained, and for that reason he is sidelined for several weeks.
"It is the third injury this football season for De Jong after he previously suffered a collapsed lung and hamstring injuries."
De Jong's absence will be a concern for Ajax as they look to hold on to top spot in the league, and their UEFA Europa League campaign gets underway in mid-February against Salzburg.
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