"I still think they are fragile defensively," said Nicholas.
West Ham have been playing well this season, but defensively they have looked vulnerable.
Slaven Bilic’s side have conceded as many as 15 goals 11 Premier League matches so far this season - more than Crystal Palace, Watford and Stoke City, all of whom are below them in the league table.
The Hammers suffered a 2-0 defeat to Watford away from home at Vicarage Road in the league last weekend.
West Ham will be looking to return to winning ways on Saturday afternoon when they take on Everton at the Boleyn Ground.
Everton are ninth in the standings at the moment with 16 points from 11 matches, four points behind West Ham, who are currently sixth.
The Hammers are just a point behind fourth-place Manchester United and are in the running for a top-four finish in the Premier League this season.