I would say it is not.
On the whole (that was the point).
If it's just about carrying on (not actually retiring) beyond a point where you really should have just retired, then yes.
But there's nothing genuinely tragic about seeing Cristiano Ronaldo fail to score in...South Arabia. He was never great enough to begin with to make it tragic.
That's the point.
He isn't on Ali's level in any shape or form (the idea that is he the greatest ever is ridiculous, nobody outside his Instagram fan club believes this).
It's a bit embarrassing, perhaps. To most (beyond his insane fan club) it's more amusing than anything. It clearly is not tragic, though - he is not, and never was, on a level which would make it so in the first place.
Whatever one thinks of Ronaldo the human being, he actually was "great enough to begin with"...in fact, he's one of the greatest footballers in the history of the game. I have Pele and Messi first and second, and some may laugh at that which is fine, but no one would laugh at the suggestion that Ronaldo is in in the top 5 of all time. Ronaldo is certainly "good enough" to be able to score a goal in the Saudi Arabia league, even at this age. Or maybe not, but it's not daft to expect that even now that Ronaldo has enough left in him to score a few goals in a league that's significantly to any other he's ever played in.
If we're going to take literal meaning of the word "tragic", then of course there's nothing tragic about Ronaldo making hundreds of millions in the Saudi league and missing sitters. No one suffers physical pain or genuine emotional sorrow if he doesn't score a goal. But in the colloquial sense of the word it is in fact tragic to see a footballer reach such a high height to fall to such a low low and miss sitters against mugs. Perhaps some will take delight in it and I suspect neither one of us have a problem with that and others will cringe and take no delight. His fanbois might be oblivious to it all and type SIUU or whatever on his Instagram feed after he posts his latest pose for the cameras.
As for Ali and Ronaldo, both are universally regarded as among the greatest of all time in their sports. I rate Ali as the greatest (I was into boxing as a kid in LA, where boxing has a fanatical following) but many boxing experts will tell you that pound for Sugar Ray Robinson was the greatest. As for football, as mentioned earlier I have Ronaldo third behind Pele and Maradona. Just opinions, but the point here is that no one disputes that Ali and Ronaldo were both in the very top tier in the history of their sports.
His fanbois will continue to like and love the photos of his WAG and his palatial pad in Riyadh, but what we're seeing now is the sad of end of a brilliant career, not too unlike the sad of a brilliant boxing career by one of the greatest, if not the greatest, in the history of his sport. But what separates these two men is that Ali saw his life in the larger context of the struggle for social and economic justice in his country, and around the world in fact; whereas Ronaldo, however brilliant he was at his peak, has never stepped off the pitch in any way to use the megaphone that could have always grabbed to try to change the world for the better.