The Premier League league leaders wanted the 27-year-old to remain on Merseyside and undertake a scan on the problem, which has been carefully managed by Liverpool, but was aggravated after a fair but firm challenge from Fernandinho at Anfield on Sunday.
However, he insisted on reporting for Egypt duty and doing the assessment with the national team.
Liverpool now face a nervy wait on feedback from the scan.
Salah missed the 1-1 draw at Manchester United following October's FIFA break as he nursed the issue and the European champions are loath to lose him as the busiest period of the season approaches.
Jurgen Klopp shed light on the nagging element of the injury earlier this month, saying: "I think it is more really annoying -- for him, not me -- the fact that it always has a bit of fluid in, and he has to deal with it, we get it out and it comes back, and stuff like that."
Egypt host Kenya in an Africa Cup of Nations qualifier on Thursday, before an away test against Comoros next Monday.