The 25-year-old suffered a torn ligament while taking a free-kick in the 1-1 draw with Southampton last weekend and was subsequently substituted.
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A three-month injury layoff for Fabio Borini leaves Sunderland in even shorter supply up front, and Moyes hinted that he could look to free agents to provide depth.
However, none of those new arrivals were attackers, leaving the Black Cats with just prolific top scorer Jermain Defoe, former Liverpool man Borini, and 17-year-old prospect Joel Asoro as registered attackers.
Sunderland have been dealt a blow following the news that Fabio Borini is facing three months out with a groin injury.
Moyes said: “Borini is out for three months, an abductor came off the bone”.
Moyes attempted to sign Steven Naismith on deadline day but could not get the deal for the Norwich striker over the line.
But they have a pre-contract agreement in place allowing the two clubs to negotiate again in January.
Borini joins long-term absentees Vito Mannone and Sebastian Larsson in the treatment room, while Lee Cattermole and Jan Kirchhoff have not managed a single appearance between them so far this season.
Sunderland next face Everton in the Premier League at the Stadium of Light as they aim to get their first win on the board.
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Meanwhile, Mannone’s deputy, Jordan Pickford, has returned from global duty with England’s under-21s with a slight thigh strain but is expected to be fit for the home clash with Everton on September 12.
