Wing Jonny May is a major doubt for England's match against Argentina on 11 November with a hamstring strain.
The Leicester player, who has scored 10 tries in nine games for the Tigers this season, picked up the injury at the England training camp in Portugal.
Harlequins fly-half Marcus Smith is on his way home after injuring a foot.
Smith is returning to London for further assessment, while Wasps second-row Joe Launchbury has taken a knock to the knee and is also a doubt for the match.
May looked guaranteed to start on the wing against the Pumas given his blistering start to the season and, with Watson likely to be rested, there will be an opportunity for international rookies Solomona and Rokoduguni, who are both expected to be fully fit after injuries to an Achilles tendon and a dead leg respectively.
Marland Yarde, who missed out on selection for the squad and has just moved to Sale, may now come into the reckoning.
"Jonny is doing everything he can to get back fit as quickly as possible. He has been playing really well, but what it means is there are opportunities for other players," England assistant coach Steve Borthwick told BBC Sport.
"Every challenge thrown our way is another opportunity.
"We are assessing the situation and getting an understanding of where all the players are at, and then I'm sure [head coach] Eddie [Jones] will make a decision."
Borthwick revealed that forwards Sam Simmonds, Charlie Ewels and Sam Underhill - as well as Solomona and Rokoduguni - have arrived in camp with minor injuries, but is hopeful all will return to full training in the coming days.
England's injury problems meant a contact training session on Wednesday afternoon was cancelled.
Meanwhile, England's forwards will take part in a training session against the Wales pack on Monday, an idea hatched on the British and Irish Lions tour of New Zealand by Borthwick and Wales boss Warren Gatland.
"It's a great opportunity for both teams," Borthwick explained.
"We are always trying to find the best way to prepare and looking for opportunities to improve. Monday is going to be a great session for us."