The Magpies travel to Stamford Bridge (kick-off 5.30pm GMT) for their first away fixture of 2019 but will be without the duo, with Shelvey picking up a thigh problem whilst Dummett is out with a reoccurring hamstring issue.
With United two points clear of the relegation zone, the pair join goalkeeper Karl Darlow among the list of absentees.
However, the Spaniard was able to reveal the return of two defenders ahead of facing Maurizio Sarri's Blues.
"Jonjo, Dummett and Darlow are not available," Benítez said. "Fede (Fernández) and (Ciaran) Clark are both available. (Florian) Lejeune, who came in against Blackburn, is fine. So, we have some good news and some bad news. (Yoshinori) Muto and Ki (Sung-yueng) remain on international duty."
Benítez recalled United's previous league meeting with the Blues - a 2-1 defeat at St. James' Park as DeAndre Yedlin's late own goal separated the two sides back in August.
And after an impressive run towards the end of last season, which saw the Magpies finish in the top ten, the Newcastle boss stressed the importance of using past experiences to build on their current top-flight position with another strong finish to their campaign.
"We were very close in our last game here (in August)," Benítez added. "People talked about tactics but they were right until the end. We have to make sure we stay in the game and if they make mistakes, we have to punish them.
"The fans, the staff and everyone here, we have to keep supporting the players. They care, they work hard, they fight. Sometimes, you have a bad moment, but the next game is another opportunity and we have to be ready for it.
"They are disappointed when you lose and don't take chances, but after that, we have to clear our heads and start thinking about the next game. Last January, we were in a difficult position, but we started winning and we finished tenth.
"It's a big city and it's a massive club. Some people say you have to do this and do that, but the reality is that when we work together and we are united, we are stronger. We saw that in the Championship and we saw that last season."
