The 28-year-old will undergo surgery and should be ready to return in time for the start of next season.
"Nothing can disguise the fact this is a massive blow because Ivan is a key member of the group but we are relieved that the injury is not a severe as we feared it could have been," Wigan manager Roberto Martinez told the club's website (www.wiganlatics.co.uk).
"The most important thing now is to think of Ivan's welfare, get the operation completed, and for him to begin his rehabilitation. Ivan is a very strong and positive character and he is determined to return to fitness as soon as he can."
Ramis, who suffered the injury in Saturday's 1-1 draw at Fulham, joined Wigan from Real Mallorca in the close season and had made 19 appearances in all competitions, scoring three goals.
Wigan sit one place above the relegation zone, ahead of Aston Villa on goal difference. (Writing by Justin Palmer, editing by Pritha Sarkar)
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