MacLeod had to be withdrawn during the first half at Murrayfield
Scott MacLeod has been ruled out of Scotland's final autumn Test with Samoa after suffering a rib injury in Saturday's victory over South Africa.
The Edinburgh second row made his first Scotland start in more than two years as Andy Robinson's men defeated the 2007 world champions 21-17.
But the 31-year-old was forced off in the first half and will now not make the trip to Aberdeen next weekend.
Loose-head prop Allan Jacobsen is a doubt with a shoulder injury.
Jacobsen disrupted the South Africa scrum throughout the contest at a wet Murrayfield as the Scots bounced back from a record defeat to New Zealand.
The Scots stood toe-to-toe with the might of the Springboks, matching the visitors physically in a battle of attrition decided by the precise kicking of Dan Parks, who scored all of the home points.
Head coach Robinson must do without MacLeod but will have been heartened by the performance of number eight Richie Vernon, who impressed when he came off the bench, with Nathan Hines moving to the second row.
Glasgow skipper Al Kellock has recently returned from a long injury lay-off and played for Scotland A on Friday but the Samoa game may come too soon for him.
Scrum-half Mike Blair, who missed Saturday's game after suffering a head knock against the All Blacks, may be back in contention if he comes through a series of medical checks.
Scotland are seeking a fifth win in six Tests following victories away in Ireland and Argentina (twice) and over the Springboks.