The Uganda international was denied a visa because he had run out of free pages on his passport.
If he is to join the team in Budapest, he must first renew his passport then head to the Hungarian Embassy for a visa before taking a solo flight on Wednesday.
"It won't be a disaster as he will have missed just the one training session tomorrow evening," Hearts boss Jim Jeffries said.
The side are also without defender Andy Webster, who is nursing a groin injury, and new signing Mehdi Taouil who is resting a knock.
Hearts take on Paks on Thursday in a Europa League third round qualifying tie.