A knee injury has forced England co-captain Dylan Hartley out of their opening Six Nations clash with Ireland.
Hartley was left out of the squad to face Joe Schmidt's men, leaving Luke Cowan-Dickie, Jamie George and the uncapped Jack Singleton to battle it out for a starting berth.
Head coach Eddie Jones said: "Unfortunately, Dylan won’t be available for the Ireland game so we won’t take him to Portugal but we are hopeful he will be back later in the championship. Owen (Farrell) will be captain by himself and he will certainly have great support from a number of senior players.”
Meanwhile, full-back Mike Brown and prop Dan Cole have returned to the group having not featured for their country recently.
Cole missed both the tour to South Africa and the end-of-year series, while Brown was dropped for the November campaign, suggesting that they weren't in Eddie Jones' thoughts going forward, but they have forced their way back in.
There is also a recall for Jack Clifford (Harlequins), while Ollie Thorley (Gloucester Rugby) is included for the first time and is one of four uncapped players selected alongside Ben Earl (Saracens), Dan Robson (Wasps) and Singleton (Worcester Warriors).
Elsewhere, props Mako Vunipola (Saracens) and Ellis Genge (Leicester Tigers), second-row Joe Launchbury (Wasps) and number eight Billy Vunipola (Saracens) all return from injury having not played for England since the South Africa tour last season.
The 22-year-old Gloucester winger has made 39 career appearances for his club and was part of England’s U20 team that won the World Rugby Under 20 Championship in 2016.
Singleton, who also won the World Rugby U20 Championship in 2016, has previously toured with England to South Africa and Argentina, with Earl and Robson joining the squad in the three-Test series against the Springboks in June.
Jones said: “We are very happy with the squad and have a number of players who have come back from long-term injury. We are looking forward to getting across to Portugal and having a good ten-day preparation for the Ireland game.”
“The first thing when we get together as a squad is to get our cohesion back. The players have been playing for their clubs with different styles and different playing philosophies, so it’s about getting them thinking about playing the England way. The second thing is to get our togetherness stronger to work as hard as we can to make sure we are well connected on and off the field so Portugal is an important camp for us.”
On England’s first opponents in the tournament, he said: “Ireland is the best side in the world. They are a very well coached and drilled side and have particular things they do well in the game. To beat Ireland, we need to compete brutally in all the contest areas of the game.”
England squad for Ireland Test
Forwards: Jack Clifford, Dan Cole, Luke Cowan-Dickie, Tom Curry, Ben Earl, Ellis Genge, Jamie George, Nathan Hughes, Maro Itoje, George Kruis, Joe Launchbury, Courtney Lawes, Ben Moon, Brad Shields, Kyle Sinckler, Jack Singleton, Billy Vunipola, Mako Vunipola, Harry Williams, Mark Wilson
Backs: Chris Ashton, Mike Brown, Joe Cokanasiga, Elliot Daly, Ollie Devoto, Owen Farrell, George Ford, Jonny May, Jack Nowell, Dan Robson, Henry Slade, Ben Te’o, Ollie Thorley, Manu Tuilagi, Ben Youngs