Tesla (NASDAQ: TSLA) shares are under pressure after a Wall Street analyst downgraded the equity, which has plunged below the key $300 level in pre-market trading.Tesla closed the previous session at$315.35 but is down 6.5% before the opening bell, trading around $294.TSLA one-week stock price chart. Source: FinboldThe sharp drop follows a downgrade from investment bank William Blair, which cut its rating on Tesla to ‘Market Perform’ from ‘Outperform’.Analyst Jed Dorsheimer explained that while markets had ...