The England international linked up with his country ahead of the Euro 2020 qualifiers with Bulgaria and Kosovo but was forced to withdraw from Gareth Southgate's squad due to illness.
The problem persisted and he was still laid low and unavailable for the win over one of his former loan clubs, Leicester City, last time out.
The stop-start opening to the campaign will have frustrated the 26-year-old, who had been pleased with his pre-season performances, including a stellar showing in the game with AC Milan in Cardiff, when he scored an excellent equaliser before the Reds went on to win a penalty shoot-out.