Wanderers are currently five points above the drop zone going into Saturday's home clash with Fulham, with Roy Hodgson's side only one point better off.
Portsmouth currently occupy the third relegation spot after Blackburn's 2-1 victory against the Cottagers on Wednesday night lifted Sam Allardyce's men up the table to 15th.
With just seven points between Manchester City in eighth and Pompey down in 18th, Megson insists very few teams can afford to relax going into the final 10 games of the season.
He told Sky Sports News: "Blackburn's result last night is a great result for them. But it didn't just take them out of the bottom three, it created an even bigger relegation battle.
"There are more teams now involved in it. The last club in the bottom three is now on 28 points so it has got a little bit closer and dragged one or two others into it.
"I think everybody is in it apart from the top six or seven."
CreepThe Reebok Stadium manager is happy that his side already have points on the board, but knows that will count for nothing if they do not continue to strive for success in the closing weeks of the campaign.
He added: "We're in a position of strength if we can use the position that we are in and keep getting one or two results and get ourselves out of this, hopefully sooner rather than later.
"What we've got to do, like everybody else, is win a game of football.
"Hopefully that will strengthen our position in terms of staying up and if results did go well for us and we creep up the table, then great.
"But we've still got to win a game of football against what I feel is a particularly good Fulham side."