Gerrard hasn't played since March, when he had surgery on a recurring groin problem, and has now been ruled out until September after picking up an infection which requires a stay in hospital for treatment with antibiotics.
The Liverpool captain is unlikely to have had any playing time before England face Bulgaria and Wales in a EURO 2012 qualifying double-header in early September.
But England coach Capello - whose side are top of their qualifying group ahead of Montenegro on goal difference - is keeping his fingers crossed that Gerrard makes a quicker than expected recovery.
"I read this and it was not good news," Capello told Sky Sports News. "Steven Gerrard is a very important player for us and also for Liverpool. It's been a long time, this injury. I hope he will return quickly because he's one of the players that makes the difference on the pitch."
Capello was speaking after attending the Preliminary Draw for the 2014 FIFA World Cup qualifiers in Brazil and he feels England have been handed a good group.
The Italian plans to step down as England coach after EURO 2012, but he believes his successor should have nothing to fear from Montenegro, Ukraine, Poland, Moldova and San Marino.
Capello expects England to be the strongest team in the group, although he warned against underestimating Montenegro after they drew at Wembley in a EURO 2012 qualifier last season.
"I think there are interesting games that England need to play against Montenegro," he said. "Also, Ukraine are the team that beat us in the last game we played for World Cup qualification for South Africa.
"I also think Poland are improving because they host the next EURO and are one team they need to respect. It will not be easy but I think that England is better than the other teams."