England skipper Ferdinand damaged knee ligaments in training
when he tackled Heskey and the Aston Villa striker fell on his left
leg.
The incident happened on Friday and was described as a freak
accident by Ferdinand.
However, Heskey has found it hard to cope.
The striker said: "I spoke to Rio afterwards and he told me
there was nothing I could do but it was still difficult for me.
"What happened was that I tried to turn the ball round the
corner and fell backwards onto him but his leg was in a position
where he couldn't actually move it.
"There was nothing you could do.
"Knowing he is out of the World Cup was very difficult.
"He is our captain and has been a great player through the years
for England and at club level.
"It was just one of those things."
Heskey is being tipped to start Saturday night's World Cup
opener against the United States despite a record of just seven
goals in 58 appearances for England.
Boss Fabio Capello believes the 32-year-old causes major
problems for opposition defences, wearing them down with his
physical style.
And Wayne Rooney and Steven Gerrard always seem to be more
effective when the burly hitman is playing.
Heskey conceded: "Forwards are judged on their goalscoring.
"People do look at that. But I like to think I bring a lot more
to the game and I do get pleasure from assisting.
"I also get pleasure from being part of a winning side.
"I do sometimes think I could have done better in certain
situations and got a goal myself but that is part and parcel of the
game."