Ferdinand was forced to pull out of United's opening Premier League fixture of the season against Birmingham City, with John O'Shea captaining the side in his absence.
Ferdinand will be have a scan on his troublesome thigh on Monday morning.
However, the United manager still felt able to put a timescale on the problem, which would make the 30-year-old a doubt for England's World Cup qualifier with Croatia on September 9.
"I would imagine Rio will be out for two weeks," said Ferguson before a match that United nonetheless went on to win 1-0 thanks to Wayne Rooney
's 99th goal from the club.
"I wouldn't think he will play against Burnley next week. I would think he is out for the next two or three games actually which is a bit of blow."
United were well short of their best though Birmingham represented only a minor obstacle and the result was not in doubt after Rooney had followed up his own shot that rebounded off the post to score from close range.
Ferdinand's pre-season had been made uncomfortable by a persistent back problem but Ferguson stressed that the centre back had fully recovered from that complaint with the thigh injury suffered while on international duty with England in Holland during the week.
Ferguson was generally content with United's slightly flat performance and backed Rooney to go on and challenge for the top scorer in the Premier League this season.
"We had some good opportunities and played some good football and in general I am satisfied with the result.," said Ferguson.
"Is Rooney capable of 20 plus Premier League goals? He is capable of that without question.
"You always need two or three of your strikers to get over the 20 goal mark. It has always been an advantage over the years for us and Wayne is capable of doing that."
Meanwhile, Ferguson confirmed Michael Owen will have chances to start for United in the coming weeks.
Owen came off the bench in the second half and only a fine save by Blues keeper Joe Hart denied him his first league goal for the Red Devils.
"Owen made a great run and the keeper made a great save. But he will get his goals, no question about that," said Ferguson.
"I started with Rooney and Berbatov today quite simply because they were at the club last season and were regular players and you've got to give them an opportunity.
"Michael will get his chances. There is no question about that. There are plenty of games coming up in the next few weeks to give him his opportunity and he will take them."
Rooney was also obviously delighted to make a winning start, saying: "I thought at times we played some good stuff. Birmingham sat back in the first half and made it difficult for us but we created enough chances to win the game.
"We couldn't get that second goal. They defended well. The second goal would have killed the game off but at 1-0 there is always a chance of the other team getting a result."