'We, as a side, rely on our openers quite a bit. A good start helps our middle order capitalise on it. There aren't many cricketers in the world who impact a game like Sehwag does. We will miss him,' Dhoni said as India open the tour with a three-day game against Somerset from Friday.
Dhoni insisted that it was important for the openers to stand up to possibly the best international attack in the world. The Test series will begin at Lord's from 21 July.
'England is a very good side, they regularly get plenty of runs. They take 20 wickets. We have to be at our very best,' he said.
The Indian captain did not allow himself to be weighed down by the fact that England, if winners by 2-0 in the series, could displace them as number one Test team in the world.
'The basis of sport is to enjoy it. A lot of times you don't enjoy sport while playing top class cricket. We don't want to get into it - the ratings aren't that important.'
Dhoni was also not ready to be overwhelmed by England's strength and also looked at a few positives due in next few weeks.
'In West Indies, it was difficult to consistently score runs. Shot-playing wasn't that easy. It could be different here. You can play shots. The outfield surely will be 200 miles faster than in the Caribbean which can be a great help to score runs,' he said.
Dhoni did not forget to express his sympathy with the victims of the Mumbai blast and hoped the resilience of Mumbaikars would help them overcome this tragedy as well.