I don't think it is serious. They taped up his ankle. No announcers in the stream I'm watching, so no real word. His movement has seemed better since then though.
My guess is that it is not serious. His main problem today so far is hitting UFEs long, especially on easy service returns he would usually be nailing. Maybe the ankle has been preventing him from turning on those serves. I think he tweaked it, but he should be ok.
2-1 and an easy service hold. Just an FYI, he has been threatening the De Voest service almost every game, but then he hits an UFE out of nowhere, and lets De Voest survive. But I would guess he has a sizable edge in total points right now.
Okay, good for him then. I'm watching the live stream right now and as you said he is making quiet a lot of UEs by hitting too long.
He looks better than De Voest but seems like he plays only at 10%