Everton midfielder Cahill, currently serving a three-match English Premier League ban after being sent off against Liverpool last weekend, is back in the national squad after a seven-month absence with a foot injury.
Grella, who is playing with Blackburn Rovers in England this season, missed Australia's 1-0 opening group win over Uzbekistan in Tashkent last month with a calf muscle injury, and is in line for his 37th international cap.
Craig Moore, a member of the 2006 FIFA World Cup team in Germany, has also been named in the provisional 35-man squad after coming out of international retirement to chase his 40th international match. Australia take on Qatar in Brisbane on 15 October.
Also returning from injury are Celtic striker Scott McDonald (groin) and young Nuremberg defender Matthew Spiranovic (wisdom teeth), who were both unavailable for the recent matches against the Netherlands and Uzbekistan.
National coach Pim Verbeek said he will monitor the fitness and performance of the players in their respective domestic league matches over the weekend, and may reduce his squad prior to the team's assembly in Brisbane next Wednesday.
Qatar lead the group on four points from Japan and Australia, both on three points, after a 3-0 demolition of Uzbekistan and a 1-1 home draw with Bahrain. Frenchman Bruno Metsu last week took charge of the Qatar national team after resigning as United Arab Emirates coach.