Freddie Woodman and Jeff Hendrick freed up two spaces after joining AFC Bournemouth and Queens Park Rangers, respectively, on loan on deadline day.
Lewis and Clark were told prior to deadline day that they would be left out of the squad but decided to turn down loan offers in the Championship.
Meanwhile, midfielder Isaac Hayden was the fifth and final player to be omitted from the squad with the 26-year-old as he recovers from a knee injury.
Here’s what Howe said on Lewis, Clark and Hayden:
“Jamal has been struggling with a long-term groin injury for probably the last year. He’s been fit, but not 100% fit.
“So he’s gone away the last few weeks and tried to get that groin right. He’s had a hamstring problem as well recently.
“So I felt with Jamal not being 100% fit to play, and Paul Dummett getting injured against Leeds, that we needed to sign a recognised left-back, and that meant then that, just with the numbers of the squad, that he had to miss out.
“As I say, he’s not been quite right, and I felt that was the right decision for the team.”
“Obviously, it’s different with Isaac, because Isaac’s injured.
“He probably won’t be back until some time in April. I think that one was slightly easier, in respect that he’s not going to be available for a long period of time.
“We’ve got Ciaran Clark, who is training with the group. His attitude has been first class. I’ve got no problem with him at all.
“Unfortunately, due to numbers, he missed out.
“I was desperate to try and get Ciaran in the 25 as well but, unfortunately, when you do the maths, someone has to miss out, and when we signed Dan (Burn) as a left-footer as well, then he gave us that option on the left-hand side.
“Difficult decisions, I love all the lads, but unfortunately in my position, you have to make some tough calls.”