Lyon is the most experienced member of Australia's current Test side and the country's most prolific Test offspinner of all time, yet this summer he has struggled for impact and has taken nine wickets at 66.66 during five Tests so far. In Pakistan's first innings at the MCG, Lyon took 1 for 115 from 23 overs, his figures ballooning as Pakistan chased quick late runs on day three.
"I'm not sure. That's up to the selectors," Smith said when asked if Lyon was an automatic selection for the Sydney Test. "He obviously hasn't bowled at his best in this game. It's always difficult bowling to lots of right-handers.
"And they [Pakistan] play spin pretty well. It's never easy bowling against subcontinent players when the ball isn't doing a lot off the wicket as well. I guess we're just looking for Nathan to be a little bit more consistent in the way he bowls."
Although the SCG has offered significant turn in some Sheffield Shield matches this summer, it is actually Lyon's worst Test venue in Australia in terms of his bowling average. In five Tests in Sydney, Lyon has picked up 13 wickets at 54.15. His overall first-class record at the ground does not make for pretty reading either, with a total of 14 wickets at 64.85 from seven games.
Australia are expected to name their squad for the Sydney Test on Friday, after the conclusion of the Melbourne Test, and Smith said there was "a good chance" that more than one spinner would be included. Left-armer Steve O'Keefe would appear the logical candidate for a recall, with Jon Holland currently sidelined by an ankle injury.
It is not out of the question that the selectors could consider a spin-bowling allrounder, with Ashton Agar and Glenn Maxwell potential contenders, although the more likely scenario is to again include a seaming allrounder. Hilton Cartwright was 12th man for the Boxing Day Test, and could yet be considered for a debut in Sydney.
That decision may in part come down to how the fast bowlers, Mitchell Starc and Josh Hazlewood especially, fare after the Melbourne Test. Both men have sent down more than 200 overs during the home Test summer and the short turnaround between Melbourne and Sydney could enter the thinking of the selectors.
"They have done some bowling," Smith said. "It's obviously been a pretty big summer for them as well - six Test matches is always a lot. They've done some yards, which is a little concerning. But I think they're pretty confident in their bodies at the moment that everything's going okay.
"At the end of this Test match is another opportunity for us to sum up where they're at. They might not end up bowling much, or at all, tomorrow. We're going to have to sum that up and see how they pull up after this Test match to see what happens in the next Test match.
"We're going to have to weigh that up. We've got Hilton here. We had him in here as cover for those quicks who had a big workload last week. They were confident this week of being able to get through and get the job done. It's going to be about summing it up and seeing where they're at after this Test match."