Farmers are due to receive their 2014 payments from December 2 this year and the combined reduction in payments could result in around 50million less going into the Scottish rural economy.
Gordon McConachie, agri-business adviser for CKD Galbraith, said:
"Farmers are now facing a situation where payments could be considerably lower than they were expecting due to a devaluation of around 24% to their SFP entitlements for 2014.
"In one instance a value of 355.16 was reduced to 273.23 a drop of some 23.07%. Net of modulation the cash position will be around 14% less.
"This has crept up on many farmers and will come as a nasty surprise on top of cereal prices being down around 40% on the year.
"Farm businesses are facing a time of unprecedented change due to CAP Reform and it is firmly in farmers' interests to ensure they have comprehensive information and advice."