Bolasie had surgery in the third week of December to repair damaged cartilage in his knee, but the ACL injury requires another operation.
"Yannick will have a second surgery at the beginning of March," Koeman told reporters ahead of seventh-placed Everton's clash with basement-side Sunderland on Saturday.
"The surgery was expected because his first surgery was about the meniscus and now what will happen at the beginning of March is about his cruciate.
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"It is difficult to put a timescale because normally a cruciate can be six, seven or eight months. We had to repair the meniscus and then wait until his knee was ready to have the second operation."
Striker Romelu Lukaku, who missed Everton's recent warm-weather training camp in Dubai with a minor calf problem, is training with the squad ahead of the visit of Sunderland, while midfielders Kevin Mirallas and James McCarthy are also fit.
Mirallas (groin) and McCarthy (hamstring) missed Everton's goalless draw at Middlesbrough on Feb. 11.
(Reporting by Simon Jennings in Bengaluru; Editing by Amlan Chakraborty)
