The 24-year-old was making his return from injury in the season opener but was forced off early on with an apparent knee problem.
Irish director of rugby Brian Smith revealed after the match that Homer had damaged his ligaments, but was hopeful that it was only a "minor tear".
"It's very disappointing as Tom has knee ligament damage. It will take 48 hours to assess it and we are just hoping it is a minor tear," Smith told reporters.
Irish staged a second-half comeback during the match but still fell short, eventually losing 20-15.