The 28-year-old was named in Jose Pekerman's 30-man provisional squad for the trip to Brazil next month, despite being out of action since January as a result of cruciate ligament damage.
"Clinically he is very well, but when it comes to football he isn't yet because he is still getting his physical qualities back," he told RCN Radio. "We have to wait to see what happens.
"He is about 60% recovered, but what he lacks is endurance, strength, speed and coordination - fundamental things for a high-performance football player."
The former Porto and Atletico Madrid forward hit 20 goals for club and country this season prior to the injury.