The country's most capped player and all-time leading goalscorer managed to get through a full 90 minutes for MLS champions the LA Galaxy in their 1-0 loss to Vancouver Whitecaps on the weekend after being sidelined with a groin injury.
Ireland take on the Scots in Dublin on Saturday in a crucial Euro2016 qualifier and O'Neill is hoping his main striker can prove his fitness for the contest.
"Ireland don't, as a rule, score many goals," O'Neill said.
"We haven't for years, and that is why Robbie has been so special for us. He's scored important goals, and you look to him thinking that, particularly at home, he might be able to unlock defenses.
"Robbie will train [with us] on Tuesday. I will have a look to see how he is. He didn't play last week [against the Revolution in MLS] because of the surface, but, hopefully, he will have come out of LA Galaxy's last game unscathed."