Gavin Henson will miss up to six weeks with a fractured cheekbone.
The centre, who joined London Welsh earlier this summer, sustained the injury during his side's pre-season friendly encounter against the Scarlets yesterday afternoon.
"London Welsh can confirm that Gavin Henson suffered a minor fracture to his cheekbone during London Welsh's pre-season friendly with the Scarlets at Parc y Scarlets on Saturday," read a statement from the club.
"It is anticipated that Gavin will return to full contact training in six weeks."
Henson played on with the complaint for 32 minutes before he was eventually replaced.