The Denmark midfielder sustained a knock at the start of the second half and was then caught on the ankle by Reading forward Andy Carroll.
The 19-year-old will finish the season on loan at the Ligue 1 club.
Teams fighting for Premier League survival, battling it out at the top or trying to get into Europe could all be tempted into the market. Arsenal The table-topping Gunners may look to add a defensive midfielder to their ranks due to growing concerns over a knee injury suffered by Mohamed Elneny in training recently. Bids have been lodged for Brighton's Moises Caicedo but it will take a big push to land one of their top targets in time.