"We wanted to see how Javier Hernandez would do in a full game and because of that we left Berbatov out and his form has been absolutely fantastic," added Ferguson.
"He has been one of our best players this season and his ability to create in tight situations would have made a difference."
Ferguson insisted players such as Hernandez, Darron Gibson, Antonio Valencia and Ji-Sung Park should have been good enough to carve out opportunities against the Scottish champions.
"We wanted to find out about one or two players but seven or eight of them played against Chelsea in the Community Shield, so we weren't short of players we needed to win the game," added the United boss.
"They should have won that game, but give credit to Rangers, their system is very difficult to break down.
"I think we played with great intensity and good commitment. But Rangers just went back to the penalty box and it was successful.
"They had two draws away from home and lost 1-0 in Seville last season so they have a successful format.
"You need 10 points to qualify and tonight was a blemish for us. We need nine points now from five games.
"If we had won everyone would have said we deserved to - we had a big percentage of the possession - but we didn't make any great chances and our first corner was after about 70 minutes, so you have to give credit to Rangers.
It was a frustrating night for us, I don't know if playing anyone else would have made any difference
Manchester United Sir Alex Ferguson
"We just couldn't get that goal. We passed the ball side-to-side but didn't cut through them."
United struggled to break down a defensive Rangers side, who fielded five defenders in an attempt to suffocate their opponents.
The home side were restricted to only a handful of opportunities, Gibson with a couple of long-range shots while returning striker Wayne Rooney had one half-chance.
"It was a frustrating night for us," said Ferguson. "I don't know if playing anyone else would have made any difference.
"They were well organised and defended so deep, it was difficult to open them up at all.
"We didn't test their goalkeeper at all, apart from a couple of shots straight at him. It was a really difficult night."
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