Rooney was stretchered off the Old Trafford field after the accidental clash with Hugo Rodallega in the home side's 3-2 victory.
Rooney was charging down a shot by the Fulham substitute, whose boot connected with the England striker's leg.
Television pictures showed a severe gash down Rooney's right leg, with blood coming from the deep wound.
Ferguson said: "It was a very bad one. He has gone to hospital. It looks like he will be out for four weeks."
Ajax has released their away soccer jersey for the 2013/14 season. Get in the Gear.
The Juventus jersey for the 2013/14 was released earlier this week. Be the first to wear the colors of the Old Lady.
The Liverpool 2013/14 soccer jersey is available for pre-order. The Reds are eager to compete for silver next season.
adidas has added some color to the Predator line with this new colorway. Released on May 17. Be the first to own a pair.
The push for more color on their cleats, adidas has added the infrared colorway to the adiZero f50 Line.
Bayern Munich are kings of Germany and hope to be crowned kings of Europe at Wembley later this month!
Chelsea won the Europa League on Wednesday. The Blues defeated Benfica 2-1 on injury time goal from Ivanovic.
Borussia Dortmund hears Wembley Calling and are headed to London for the Champions League final.
The new PUMA evoSPEED 1.2 FG. A great new soccer cleat with classic look and first time for PUMA to be on the cleat.
One of the top soccer cleats for control the Nike CTR360 will not let you down on the field in tight spaces.