Bilic has earned the backing of Hammers fans since taking charge at the start of the season.
The Croatian boss has received plenty of plaudits for helping West Ham to improve their style, making them more pleasing on the eye than they were under Sam Allardyce, but Nicholas isn’t totally convinced by the former Besiktas boss.
Nicholas says that Bilic hasn’t managed to progress the side enough as yet, and claims that there are still problems which are evident in the Hammers’ team.
"I think he’s come through tests, but I don’t think he’s come through them well," Nicholas said.
"I refer back to the game when Bournemouth beat them 4-3, and you knew that there were real issues there.
"It was the home form [that was the problem], because the away from speaks for itself.
"We have seen with Sam Allardyce in the past that he could win at home, and he would get booed. Bilic is one of their own, but you have to be giving them something that looks like it is moving the team on. I don’t think he’s given them that. There’s pressure on him to be bolder."
West Ham made a flying start to the season, but their form more recently has offered cause for concern.
Bilic’s side have failed to win any of their last four matches, and they will be keen to get back on track as quickly as possible.
Unfortunately for West Ham, their next match looks to be another tough test as they have to take on title chasing Manchester United.
The Red Devils have not been at their best this season, but they are still near the top of the Premier League table and are a formidable opponent at Old Trafford.