RICS said some lenders have reviewed their policies to decline loans against affected properties, and some sales were not being completed as a result.
The institution claimed that with correct treatment, knotweed need not be a "life sentence for a property" and should be assessed in a similar way to subsidence and asbestos. RICS is consulting on this to develop best-practice guidelines.
RICS representative Philip Santo said: "A standard risk assessment framework is being proposed to help valuers provide more informed advice to their clients and to enable lenders to adopt more balanced policies.
"As the treatment industry develops and matures, it is hoped that Japanese knotweed will soon become just one more consideration in the complex valuation process. The consultation aims to canvass opinion to help make this happen."
RICS is inviting responses from members, lenders and treatment experts. The consultation runs until 9 December and can be found at consultations.rics.org/consult.ti/japaneseknotweed/consultationHome.