Nick Knight told Sky Sports that Essex could be a big threat at Friends Life t20 Finals Day.
The Eagles defeated Nottinghamshire by 47 runs at Trent Bridge on Thursday to cement their place at Edgbaston on August 17, where they will face Northants in the semi-finals.
Essex have had their troubles this season - bowled out for 20 in County Championship cricket by Lancashire and skittled for 74 in a FLt20 group encounter with Middlesex.
But after watching Australian quick Shaun Tait collect a hat-trick in Nottingham and the big-hitting Ryan ten Doeschate smack a 44-ball 82, former Essex opener Knight feels the Chelmsford outfit are "a side to be reckoned with".
"Essex have been inconsistent and it must be infuriating for [coach] Paul Grayson but if you look down that side you do feel threatened by them," said Knight, who played in 100 one-day internationals for England.
"They have Tait, Graham Napier is having an outstanding season and James Foster is still one of the best, if not THE best, 'keepers around, while they also have Ten Doeschate, Ravi Bopara and the power up front with Hamish Rutherford.
"They are a side to be reckoned with".
Ten Doeschate came to the Trent Bridge wicket with Essex creaking at 46-3 but put together a 72-run stand with Bopara (38) for the fourth wicket and Knight applauded the Netherlands international's game management.
"Essex struggled a little bit up front and lost a couple of wickets and it was the partnership with Bopara that really got Ten Doeschate going," added Knight.
"He scored fours and sixes but in between he knocked the ball around beautifully; there were very few dot balls and the momentum was with Essex."
Defending FLt20 champions Hampshire will play Surrey in the second semi-final at Edgbaston, with the counties overcoming Lancashire and Somerset respectively in their last-eight clashes earlier in the week.
And ex-Surrey supremo Chris Adams says The Oval side will have their work cut out against the Royals, who will take part in their fourth successive Finals Day and also hold the domestic 40-over crown having bested Knight's former employers Warwickshire last year.
"Hampshire are running hot with [Michael] Carberry leading the way and they have been putting together some really solid performances in one-day cricket for a number of years now," he said.
"They consistently find their way to Finals Day, consistently put big score on the board and consistently defend them. They will be everybody's favourites at Edgbaston."