The Serbian defender was withdrawn during United's opening-day win at West Bromwich Albion, and although initial estimates put him out for six weeks, the Scot has said that he is no closer to a return.
"It's slow progress with Nemanja," said Ferguson.
"Calves can be troublesome. He's not done any training [and] he's not making any great progress at the moment."
Premier League leaders United will try to maintain their 100% start to the season at Stoke City on Saturday.