Ronaldo has missed Portugal's last two World Cup warm-up games against Greece and Mexico because of knee and thigh injuries that hampered his involvement in Real Madrid's end-of-season run-in.
But the 29-year-old, who helped Real to UEFA Champions League glory last month, returned to training on Friday and will be hopeful of gaining some match practice before the tournament gets under way on Thursday.
And his prospective comeback will come as a timely boost for Paulo Bento's men, who will look to build momentum ahead of a daunting World Cup opener with Germany a week on Monday.
However, Portugal may have to cope without midfielder Raul Meireles because of a muscular problem, while defender Pepe is continuing his recovery from a leg injury.
Portugal have been unconvincing in each of their previous two games, playing out a dour 0-0 draw with Greece before beating Mexico 1-0 on Friday thanks to an injury-time effort from defender Bruno Alves.
Bento will want his team to produce a much better display on Tuesday against an Ireland side re-building ahead of their qualification campaign for UEFA Euro 2016.
Ireland are winless in their last five matches under coach Martin O'Neill, but should head into the encounter at MetLife Stadium in New Jersey with confidence following decent results against World Cup participants.
O'Neill's men held four-time winners Italy to a 0-0 draw late last month and claimed a 1-1 stalemate against Costa Rica on Saturday.
Portugal, who have been drawn alongside Ghana and United States as well as Germany in Group G, will expect a stern test from Ireland, and Bento is eager for his side to use the game to eliminate the errors in their play before the start of the World Cup.
"It's going to be a balanced group with four strong teams so it's going to be very difficult for us," Bento said after the win over Mexico.
"But we will fight to the end to achieve our first goal, which is to reach the knockout phase.
"We still have a few mistakes that we need to correct before the World Cup."
