One solution would be hand Gloucester's Billy Twelvetrees his international debut alongside Brad Barritt in the midfield.
Alternatively London Irish's Jonathan Joseph or fly-halves Toby Flood or Owen Farrell could switch to centre.
At 6ft 3in tall and almost 16 stone, Twelvetrees certainly has the physical presence required at international level and Lancaster is convinced the 24-year-old could cope if called upon.
"I'm not sure there is a like for like replacement for Manu so he is a big loss," said Lancaster.
"If you look at his performance against New Zealand he was outstanding. But this time last year he didn't play in the first two games because of a hamstring injury.
"We want to make sure he doesn't break down again. Everything I've heard points to the fact he will be running fully and changing direction by this weekend. The medical staff have every confidence he'll be training fully next week.
"One of the options is to play Jamie (Joseph) at 13. He's been playing full-back for London Irish for the last three or four weeks.
"I don't think it's too early for Billy Twelvetrees to come in. I don't think I've worried in the past about that.
"I don't see a lack of international experience as a barrier to selection, it's about what's best for the team.
"I haven't worried in the past about picking uncapped players. This time last year there were seven new caps."