Although both Moody and Bath head coach coach Steve Meehan initially played down fears the openside would be sidelined for a significant period after the Heineken Cup win over Aironi, it has now emerged he has damaged his medial collateral ligament.
Bath confirmed on Tuesday that he had suffered an injury to the medial collateral ligament after twisting his knee.
"Lewis took a knock to his knee at the weekend, which is slightly more serious than first thought," said head coach Meehan.
"It is frustrating for us to lose him at this stage in the season, but it does mean that other players in the squad get the opportunity to come on in his place and show us what they can do.
"We will of course make sure he receives the best medical attention to get him back on the field as and when he's ready."
Moody's injury opens the door for a specialist openside flanker to make their mark in the Six Nations.
South African-born Hendre Fourie would appear to be in pole position having been used as cover for Moody during the autumn internationals.
Other candidates include Saracens uncapped youngster Andy Saull, London Irish's Steffon Armitage and Northampton's Tom Wood who has been in outstanding form since joining from Worcester.
Whoever it is, Johnson has promised them that Moody will not automatically return to the team upon his return.
He said: "It is always disappointing to lose a player and leader of Lewis' calibre.
"But, as I have consistently said, good teams adapt to injuries and that is what we intend to do.
"While this could still mean Lewis plays a role in the Six Nations, it does mean that another player gets the chance to step up and make it hard for him to get the shirt back."
Johnson's other dilemma is who will inherit the captaincy. Veterans Mike Tindall and Nick Easter - who led England against Samoa in the autumn - would appear to be the favourites.
An announcement will be made in the week building up to England's Friday night trip across the Severn Bridge to face Wales on February 4.