After a recent winning streak, the S&P/ASX 200 Index (ASX: XJO) is coming back to earth this Wednesday. At the time of writing, the ASX 200 has lost a meaty 0.47% and is back down to around 8,455 points. But let's talk about what's happening with one particular ASX 200 stock.  

That ASX 200 stock is none other than Goodman Group (ASX: GMG). To put it bluntly, Goodman shares are having an awful day. This real estate investment trust (REIT) closed at $38.12 per share yesterday afternoon. But today, those same shares opened at just $36.60 before falling to the current $36.40 price. That's a drop worth a nasty 4.54%.

Big pricing drops like this aren't exactly rare for Goodman Group. Although this ASX 200 stock is up a whopping 45.3% or so over 2024 to date, it has also had a few rough patches, including a 7% one-day plunge back in early August.

Check all that out for yourself below:

So, what on earth is going on today that has resulted in this chunky, market-trailing loss for Goodman Group?

Why is this ASX 200 stock down more than 4% today?

Well, it's hard to know with absolute certainty what's going on with Goodman Group this Wednesday, as there haven't been any fresh ASX announcements from the REIT itself. However, some news is floating around that probably explains what's going on.

According to reporting in The Australian today, a major investor in Goodman Group has reportedly executed a massive block sale of shares. That major investor is China Investment Corporation (CIC), which is a sovereign wealth fund of the People's Republic of China.

The report reveals that CIC offloaded a $1.9 billion parcel of shares in Goodman this week, representing 50.4 million shares or 2.6% of the company.

This block sale was done at an auction, with buyers able to pick up the shares for between $37.55 and $37.60 each. This sale represents the first time that CIC, a long-term investor, has reduced its position in Goodman shares since 2012. After this sale, the wealth fund still retains an approximate 6.3% stake in the ASX 200 stock. 

With a share sale of this magnitude, it's perhaps no surprise that the Goodman share price is under significant pressure today, on a day of broad market selling no less. The sheer volume of the block sale certainly has the potential to upset the supply-and-demand balance in the markets this Wednesday, which is the likely culprit behind the big drop in value we are witnessing.

Let's see how this ASX 200 stock fares over the rest of the trading week.