Brighton and Hove Albion head coach Roberto De Zerbi said the injury to Solly March was the 'worst thing' after their 2-1 loss to Manchester City last Saturday.
March, went down in the second half after twisting his right knee and had to be stretchered off.
It's a huge blow for the player and the team as De Zerbi is already without established left back Pervis Estupinan, who sustained an injury at Aston Villa earier this month.
Brighton face Ajax in the Europa League on Thursday night and this Sunday they are back in Premier League action as they welcome Fulham to the Amex Stadium.
Here's the options to cover at left back for the vital matches ahead...
1. Pascal Gross
The experienced German can play anywhere at anytime. The left back slot is not new to Albion's utility man but his experience and guile would be missed from midfield Photo: Alex Pantling
2. Igor
The £15m summer arrival from Fiorentina is mainly a left-footed centre half but has played the left back role previously and could easily slot in to face Ajax Photo: Mike Hewitt
3. James Milner
The 37-year-old had a tough time at right back last Saturday against Doku at Manchester City. More than capable of playing at left back back and could be a reliable option for the coming matches Photo: OLI SCARFF
4. Tariq Lamptey
The full-back was one of the best players on the pitch at Marseille in the left back role. Mainly a right back but for me Lamptey makes the most sense, if he is fit enough to play Photo: Mike Hewitt