Warriors had earlier announced the signing of the USA centre Folau Niua but the extent of the Van der Merwe's injury cast a damper over proceedings. The Edinburgh winger Lee Jones had been signed on loan as cover for the Canada internationalist last week and they further eased their injury problems with the signing of Niua to 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 international sevens tournaments, has been brought in to replace Gabriel Ascarate, who left last week after a neck injury ended his season.
Niua, who won his three full caps for USA last year, said: "I've played against Leone Nakarawa and Niko Matawalu on the sevens circuit and I also 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."
Townsend was pleased with the signing. He said: "Folau is an exciting player with a lot of experience. He had a cracking game against the New Zealand Maori team at the end of last year and is a real ball-playing centre and also a very effective ball carrier."