The S&P/ASX 200 Index (ASX: XJO) had a mixed five days last week. But thanks to a strong finish, the benchmark index was able to record a very small weekly gain to end at 7,308.6 points. Unfortunately, not all ASX 200 shares were able to push higher with the market. Here’s why these were the worst performers on the index: Collins Foods Ltd The Collins Foods share price was the worst performer on the ASX 200 with a 13.1% decline. The quick service restaurant operator’s shares actually stormed to a record high following the release of its full year results, before starting to sink. This may have been driven by a couple of broker downgrades. Largely on valuation grounds, UBS and Morgans downgraded the company’s shares to neutral/hold ratings.