The team is still awaiting the test results.
A former first-round draft pick in 2008, Otah has missed 31 of the last 35 games with left knee problems. He started four games last season before eventually winding up on injured reserve for the third straight year.
Otah is listed at 330 pounds in the media guide.
When asked if Otah looked heavier this year, Rivera responded "I think Jeff looked like Jeff" and "he's a big guy."
The Associated Press contributed to this report.