"But if I can come on and make an impact like I did I'll do that."
Defoe said last week he would be content to make an impact from the bench if Capello thought that was where he could do most damage and the Spurs man reiterated that after his latest goal-scoring exploits.
"At the minute, everything I hit seems to be going in, I'm delighted," he said.
"With England you are playing with good players so you get the opportunities.
"The manager picks the team. I'll just keep working hard and see what happens."
England know victory over Croatia on Wednesday will book their place at the World Cup in South Africa 2010 and, rather than gamble on starting Defoe, Capello is likely to use him as an substitute again.
The Italian has tended to favour a big man to play alongside Rooney and Capello revealed he was pleased with the way Heskey performed in the first half against Slovenia.
I was not happy to concede a late goal because the concentration was not good in the last four or five minutes
"I'm happy because I learned a lot of things," said Capello.
"Friendly games are always important to study the players. I wanted to see a lot of players because playing at Wembley is not the same as playing for their club.
"Heskey played a good game, then we changed it at half-time to see the different style of play, with two little players up front. They played well.
"I wanted to know a lot of things. This isn't a friendly game, it's really important."
Against Slovenia a first-half penalty by Frank Lampard and Defoe's 62nd-minute strike had England looking comfortable until Zlatan Ljubijankic reduced the arrears six minutes from time.
"I was not happy to concede a late goal because the concentration was not good in the last four or five minutes," said Capello.
"We played too slow, we played long balls and didn't play the style I like.
"I want the players to focus and concentrate on every minute of the game."
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