Milos Raonic was out of tennis for a very long time before making a comeback earlier this year during the grass season. He surprised many by coming back, as nobody really expected it, and he didn't really tease it on social media either.
It just sort of happened, and while it didn't look spectacular, it looked fair enough considering the circumstances. He won a match on his comeback and won a match at Wimbledon as well. Good play did happen, though, but it was at the Canadian Open in Toronto, where he played in front of family.
He bested Frances Tiafoe in the opening round and advanced to the 3rd round, where he lost to Mackenzie McDonald. It was a very emotional tournament for Raonic, who wasn't sure whether he would continue his career as his body was unlikely to be able to keep up with the demand of playing regularly.
He took part in the US Open but lost in the opening round, after which he took part in the Laver Cup as an alternate. It was an event in Canada, so it made sense, but he didn't play as he wasn't needed. Team World demolished Team Europe easily.
He hasn't played since then, and it's unlikely that he'll play at all anymore, especially after withdrawing from this event. There is still a lot of uncertainty regarding his tennis career, but he's basically retired in all but name.
It's very hard to imagine that hell actually commits to playing regular tennis again, especially since his body doesn't seem likely to hold up. We'll see as he's yet to formally retire but what we do know is that he won't be in Basel.