Vardy rested while England played their recent World Cup qualifiers, but Leicester boss Craig Shakespeare said he has looked sharp in training.
Shakespeare will also have a fully-fit Jamie Vardy available against West Brom, the striker having recovered from an ongoing hip problem during the global break.
The striker was injured in last month's 1-1 draw at Huddersfield but played in Leicester's next two matches with the help of pain-killing injections.
'Vardy has fully recovered from his hip problem, ' Shakespeare said. 'He had injections and was given time away.
The 30-year-old has been Leicester's top scorer in the past two seasons and is already in the goals this term despite the club's slow start to the campaign.
Manufacturing boost fails to lift 'muted' economy, survey finds
Its employment expectations, investment in training and confidence in profitability and turnover have also stayed much the same. Hiring difficulties were facing businesses across both sectors.
"It is always a unusual week global week but playing Monday has helped us this time in terms of getting everyone back and getting a clean bill of health", Shakespeare told club website.
Leicester City now sit 17th in the English topflight with just five points from seven games.
Simpson has been ever present in the Premier League this season and is odds-on to be in the line-up when West Brom visit the King Power Stadium.
The Leicester boss confirmed Wilfred Ndidi was fit despite appearing to injure his hamstring on worldwide duty with Nigeria while Ben Chilwell is also available after missing England Under-21 duty with a knock. He's fine so there's no problems there'.
West Brom are 10th in the league with nine points from seven league games.
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