Second-placed United are four points behind the Blues going into Sunday's clash at Stamford Bridge.
The Red Devils have fallen behind in eight of their 12 matches so far this season, and Giggs believes that they will get punished by the league leaders if they concede the first goal at the weekend.
"There are two ways of looking at it," said Giggs. "Obviously we are pleased that we are able to come back and have shown great character in those eight games.
"But you cannot keep relying on the lads up front to score the goals. It is something we have looked at and are still looking at.
"It has happened again against Braga but against Chelsea if we go behind it will be tough to come back."
United travel to Stamford Bridge and face Chelsea at 4pm on Sunday.