WESTERN Bulldogs forwards Robert Murphy and Brad Johnson could be missing for the next three weeks, a cruel blow for the team that got its season back on track with a strong win over the Sydney Swans last weekend.

Murphy will undergo arthroscopic surgery on his right knee on Monday night to remove a small cyst at the back of his patella tendon.

The club expect Murphy to miss between two and three weeks.

Johnson didn't play in Saturday win over the Swans, but experienced tightness in his achilles tendon after a training session and is expected to miss at least three weeks.

The Bulldogs have a tough three weeks ahead with matches against North Melbourne, Fremantle and Collingwood to come.