Since winning 3-1 at Liverpool on December 15, Villa have suffered three heavy defeats in a row, conceding a total of 15 goals and failing to score once themselves.
"Everyone was positive after the Liverpool win but there is now a negativity after these three defeats," Lambert said. "I understand that feeling but I have a belief that Aston Villa will be fine. The big disappointment is that there are a lot of experienced players out of the team."
He added: "Andreas Weimann had to play at the last minute against Wigan despite having a leg injury. Once we get everyone back in January we will have to wait and see what happens.
"We had a decent spell in the first half when we looked like ourselves. We had a couple of half chances but in the second half there was no creativity. That was hard to take for sure.
"I will speak to the chairman to see what is happening in regard to bringing in some new players. I always knew it was going to be a massive job at Villa. It is a massive football club with a great tradition."
He said: "It was a really tense game before it started as both Villa and ourselves are in a similar position. We tried to play in the right way and the result was very important.
"In terms of the performance I thought it was similar to that we showed against Everton and Arsenal in the last two games.
"We were very clinical in both boxes and defended well, keeping (Christian) Benteke quiet. He is a footballer who can make a difference at this level. We covered this threat really well and had very good concentration."