Van der Merwe has shoulder surgery
Glasgow winger DTH van der Merwe faces up to six months on the sidelines following shoulder surgery.
Warriors announced the signing of United States centre Folau Niua earlier on Monday but there was bad news to come as they confirmed the extent of the Canada international's injury.
Glasgow last week signed Edinburgh winger Lee Jones on loan as cover from Van der Merwe and they further eased their injury problems with the signing of Niua until the end of the campaign.
The 29-year-old will join Gregor Townsend's squad this week, subject to a visa and medical, after leaving the USA Eagles sevens team following their Shield success at the Wellington Sevens in New Zealand.
The California-born player, who has scored 239 points in 21 sevens tournaments for his country, has been brought in to replace Gabriel Ascarate, who left the club last week after a neck injury ended his season.
Niua, who won his three full caps for the US last year, said: "I've played against Leone Nakarawa and Niko Matawalu on the sevens circuit and they're very good players and I enjoyed playing at Scotstoun with the USA sevens team at the Glasgow Sevens last year.
"I've been playing a lot of sevens recently, so I'm fit and ready to play games.
"It'll be the first time I've played for a club in Europe, but if things go well I'd love to stay in Glasgow beyond this season."
Head coach Townsend, whose team maintained their RaboDirect PRO12 top-four hopes with an 8-6 win over Connacht on Sunday, said: "Folau is an exciting player who has a lot of experience, having been a regular for the USA sevens team for the past few years and now with three caps for his full national team.
"He had a cracking game against the New Zealand Maori team at the end of last year and is a real ball-playing centre who is also a very effective ball carrier."