Lester injured his foot in the Lions' Round 3 clash against Melbourne, with preliminary scans indicating a partial rupture of the Linsfranc ligament in Lester's right foot.
Further scans taken late last week determined surgery the best option for Lester.
"Unfortunately scans last week showed that Ryan had ruptured the Linsfranc ligament, which is the ligament that stabilises the first and second metatarsal - essentially, his two largest toes," said Dean Warren, General Manager of Football Operations.
"This did require surgery, which was performed successfully yesterday. A screw was placed in the ligament and Ryan will be in a cast for seven days."
"This is obviously a blow for Ryan who will now spend the next 16-20 weeks recovering and will consequently miss the rest of the season."
Lester came to the Lions with pick No. 28 in the 2010 AFL National Draft and made his debut for the Club at his first opportunity in Round 1 this year.
To view the Club's current injury list, click here.
