A Vestas spokesman was unable to comment on the exact reasons behind Rieks' leaving the company other than to say it was a "board-level decision". He will be temporarily replaced by Vestas chief executive Ditlev Engel.
Riek's was previously Vestas president for Central Europe and was moved across to the offshore division by Engel on 20 January. He replaced Anders Soe-Jensen.
Vestas confirmed Rieks was no longer employed by the company. He follows Henrik Norremark, who was CFO and had been made deputy CEO as part of the January restructure, and who stood down yesterday.
It was also revealed chairman Bent Carlsen and deputy chairman Torsten Rasmussen have informed the board they will not be seeking re-election in March.
The latest restructure, only weeks after the last, came as the company announced a series of disappointing financial results.
It missed its revenue target for 2011 by 16% amid what the company describes as a "challenging year".
The 2011 revenue figure of €5.8 billion also falls below Vestas' own preliminary financial figures in January. It also posted an operating loss of €60 million.