Assumptions about the mid-term trajectory for crude oil prices means the economy of Saudi Arabia may face significant pressures, Fitch Ratings said Tuesday.

The credit rating agency said it downgraded the long-term rating for Saudi Arabia one notch from AA to AA-. Structurally, the Saudi economy is weaker than its peers and economic growth for the oil-rich kingdom is expected to slow considerably.

The ratings agency said it expected the price for crude oil would average $35 per barrel for 2016 and increase to $45 per barrel by next year. Using the global benchmark Brent as a standard for reference, the forecast from Fitch is nearly 20 percent below the level during trading early Tuesday. If its price assumption holds true, Fitch said there would be "major negative implications for Saudi Arabia's fiscal and external balances."

Saudi Arabia is among the oil-rich nations considering a freeze in oil output. Russia and some members of the Organization of Petroleum Exporting Countries are set to review the prospects during a meeting this weekend in Doha.

Crude oil prices started moving lower in mid-2014 as U.S. crude oil production skewed markets toward the supply side. Decisions from OPEC in late 2014 and in December to keep output steady added further downward pressure to crude oil prices moving into 2016.

Rumors of some form of an agreement in Doha, however, have led to a major rally in crude oil prices, which are up 11 percent since the start of April. Saudi comments that it would cut production if other market players participated sparked a major decline in prices last week. Iran said it would hold output steady, but only after it retakes a market share lost to sanctions.

The move by Fitch is the second so far this year for Saudi Arabia. Standard and Poor's in February lowered the sovereign rating one notch from A+/A-1 to A-/A-2 because of lower crude oil prices, which the ratings agency said would have a "marked and lasting impact" on the kingdom's financial position.

For fiscal year 2015, the country reported total revenue at $162 billion, an estimated 15 percent decline from budgeted revenues.

The government in December said it was setting up a $48.7 billion stimulus package to support projects designated as national priorities because of "excess" volatility in crude oil prices. Saudi Aramco, the world's largest oil company, announced plans to list its shares on the public market for the first time as part of a government reform agenda that includes privatization of some economic sectors.

Fitch Ratings said it expected the Saudi economy to grow by 1.5 percent this year and 1.7 percent in 2017, compared with a 3.5 percent growth rate reported in 2015.