At the height of the Catalan independence drive in mid-October, the central government in Madrid had lowered its 2018 growth forecast to 2.3 percent from 2.6 percent, a marked decline from the 3.1 percent expected for 2017.
"If we recover normalcy, stability and calm, this 2.3 percent growth will be three percent next year," Rajoy said at a meeting of his conservative Popular Party (PP) in Mataro, near Barcelona.
Madrid has ordered new regional elections for Catalonia on December 21 after ousting the government of former Catalan leader Carles Puigdemont and suspending the parliament over the independence bid.
International agencies including the IMF and the OECD have warned of the financial fallout of the crisis for the eurozone's fourth-largest economy.
Catalonia generates about 20 percent of Spain's GDP, and tourism along with retail and new car sales slowed in October after the parliament's declaration of independence.
The campaign for the new elections officially opens on Tuesday and opinion polls show that pro- and anti-independence forces are running neck and neck, an outcome which could make it difficult to form a viable regional government.
During the last elections in 2015, Rajoy's PP obtained just 11 of the 135 seats in the Catalan parliament.