Fighting the dark forces is not so profitable in Europe
The group, which sells and makes fantasy tabletop wargames, blamed lower sales in France and Germany for its problems.
Shares in the UK firm sunk to a 12-month low before recovering slightly to settle at 258p, down 21.2%.
The firm is closing 35 loss-making stores and cutting staff by 10%.
The cutbacks will cost about £6m to implement, but are expected to result in annual cost savings of £7m.
They are designed to "address short-term issues", according to Games Workshop management, who "remain confident in the long-term future of the business".
Second profit warning
The warning that full-year earnings will disappoint is the second this year.
In January, the Nottingham-based company, which employs some 2,800 staff and has 347 stores worldwide, including 120 sites in the UK, said flagging demand over the Christmas period would result in lower sales and earnings than expected.