The 30-year-old defender, Celtic's longest-serving player, was injured in the build-up to Ludovic Giuly's decisive second goal in Barça's 3-1 win in Glasgow. Although the injury is not as bad as first feared, McNamara's enforced absence is still a major blow for Celtic and Scotland.
McNamara is out of the 29 September trip to AC Milan and could miss the double-header against FC Shakhtar Donetsk, as well as Scotland's FIFA World Cup qualifiers against Norway and Moldova in October.
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