On Sunday, Waitrose unveiled the first details of its home delivery service in London, which will commence from mid-March.
The news followed the sale of two million shares at 254p by Ocado CEO Tim Steiner on Friday evening at a value of £5m, less than a year after the company's flotation.
This prompted Shore Capital analyst Clive Black to question the timing of the disposal on Monday and warn Waitrose now represented a "major potential challenge".
At 205p as The Grocer went to press, Ocado's share price has fallen by 23% since JLP sold its last 10.4% stake on 11 February at 265p. For an initial investment of £65m, JLP made total gains of over £250m.
But the biggest falls were this week and appeared to follow Steiner's share sale. A City source said: "Steiner's decision to sell appears to rule out bid rumours from the share price. It's unfortunate that JLP's announcement followed so swiftly."