The Wales star missed Monday's session due to illness but was able to work as normal with the Real Madrid squad as the club prepares to take on Pep Guardiola's side.
The former Tottenham star was forced to sit out a routine practice session on Monday after suffering from flu-like symptoms, throwing his participation in Wednesday's clash at Santiago Bernabeu into doubt.
However, the club has confirmed he was able to train as normal early on Tuesday and will be available for selection to coach Carlo Ancelotti.
The news comes as a major boost to Madrid, which also welcomed back Cristiano Ronaldo and Sergio Ramos to training on Monday after they recovered from hamstring and neck injuries respectively.
Defender Alvaro Arbeloa and forward Jese Rodriguez remain the only injury absentees for Wednesday's encounter.