The 36-year-old veteran of three World Cups with Argentina is suspended after being sent off in last weekend's 1-0 win at Huracan that put River alongside four other teams at the top of the Apertura championship after two matches.
When Ortega, who has a known drinking problem, missed Tuesday's practice there were fears of a relapse without a match to prepare for.
His unavailability, though, gives coach Angel Cappa the problem of finding the right replacement for River's best player of the opening matches of the season.
A victory at their Monumental stadium would further cement River's fight against a poor relegation average and raise hopes of playing for their first title since the 2007/08 Clausura.
"Our mentality is to win. We have to play each match like a final," Almeyda told reporters.
"I never understood the business of the averages. For me it's like a race, you take off and have to win, not look back. Winning you get the largest number of points and so fight for the championship."
Independiente, whose last title was the 2002 Apertura, have only picked up one point to River's six as they rebuild under new coach Daniel Garnero having vied for last season's Clausura until the closing matches in May.
They won both teams' meetings last season with a 2-0 victory at the Monumental in March.
