The Portugal winger grabbed a double in Tuesday's 3-2 Champions League defeat to Galatasaray, giving Jose Mourinho's side a 5-3 aggregate win to set up a semi-final against Borussia Dortmund.
Ronaldo picked up an injury late on in Turkey, and sat out Thursday's training session.
But he was involved in Friday's session at the club's Football City base and looks set to feature at San Mames, where Madrid clinched last season's title.
Michael Essien appears unlikely to play a part after he was forced off in the first half in Galatasaray and has not taken a full part in training since, but Xabi Alonso and Sergio Ramos are available after being suspended for the second leg of the European tie.
Madrid have left themselves too much to do in their pursuit of Barcelona at the top of La Liga, but have been on a superb run of form which has seen them lose just one of their last 13 league fixtures.
Victory this weekend would also be a landmark for Mourinho as it would move him into outright third place on the list of the managers with most wins in charge of Los Blancos.
Bilbao, in contrast, have had a difficult campaign, failing to build on the promise of their performances in Europe and domestically last season.
The Basque club are nine points clear of the drop zone, but midfielder Markel Susaeta believes victory over Madrid would make up for some of the disappointments experienced this season, and help give their San Mames home a good send-off ahead of the club's move to a new ground next season.
He told Marca: "San Mames deserved something more from this season.
"We had a difficult season in Europe and in the cup, and also we are not doing the best season in the league, far from it.
"And what better way to give joy to our fans, to San Mames and ourselves than by beating Real Madrid.
"They have some of the best players in the world and we will need a perfect performance.
"These games are always special and with it being the last Athletic-Real Madrid game in the old San Mames, we have even more incentive to play well and get the three points."