LinkedIn, which had a successful IPO earlier this year, should see a major impact to its stock price in the coming week. Despite listing at a relatively high valuation, LinkedIn has gained around 74% since its IPO on May 19, 2011. Much of the increase can be attributed to the low float. Less than 10% of LinkedIn’s total stock is currently tradable in the open market.

However, on November 21, LinkedIn’s lockup period for its shareholders will end, triggering a potentially huge selloff in the market. LinkedIn’s float is expected to increase significantly next week. Some analysts expect it to more than triple.

LinkedIn’s stock is down around 5% today, following speculation of a highly probable selloff on November 21.

Many of LinkedIn’s early investors and employees are expected to liquidate at least part of their positions in the coming weeks. This will likely spawn a lot of newly minted “LinkedIn millionaires”. Following LinkedIn, even Groupon IPOed earlier this month, and its stock is currently trading at a significant premium to its initial price. Even Zynga is expected to IPO by the end of this month.

Disclosure: I don’t have any open positions in LinkedIn, but I’m very inclined to go short on it.