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His last appearance for Ireland therefore was a man-of-the-match performance in the narrow defeat to New Zealand last autumn, while he has played just a bit-part role for Leinster this season.
But O'Brien, who has returned to training, believes he could yet feature for Leinster before the campaign finishes and prove his fitness ahead of Ireland's trip to face the Pumas.
"I don't know what Joe's [Schmidt] plans are (for Argentina) or anything like that," he told the Irish Independent.
"I will have to speak to him about that and see what he's thinking if I am fit. I am presuming he is going to rest some lads going over there to keep them fresh for next year.
"I'm into my second week now of hard training. I'll know where I am in two more weeks. I'll probably know then exactly when I'll be coming back.
"I've just been doing a lot of running and strength and conditioning, trying to get back into reasonable shape to give myself the best chance of getting back at some point, either at the end of this year or in the summer."