There's been reports today saying he's out until 2022 but with no further detail.
https://theathletic.com/news/brighton-suffer-injury-blow-as-lewis-dunk-is-ruled-out-for-rest-of-year/1e3zuxBaRr4i/
The game is available in full now (the full 100 minutes !) on demand on Sky/Now TV
There’s an interesting bit of commentary where they suggest Gross was upset at being subbed and went “straight down the tunnel”. (This was just after they showed that Gross gave a normal routine handshake with...
That was a very strange h/t warm up / small sided game but he was putting in just as much effort as the other 8 subs who were mostly rooted to the spot.