The Saracens lock has captained England in every Test since Martin Johnson took charge of the team in 2008, but came under fire for his performances in the autumn internationals.
Johnson initially named his 32-man elite performance squad without identifying a captain, but confirmed Borthwick’s appointment at the team’s pre-tournament training camp last night.
The coach, meanwhile, is sweating over the fitness of blind-side flanker James Haskell, who is awaiting the results of a scan on a knee injury sustained on Heineken Cup duty for Stade Francais at the weekend.
Five players have been brought in as cover with props Matt Mullan, of Worcester, and Leicester’s Dan Cole replacing Andrew Sheridan and Julian White for the Portugal trip.
Back-rowers Dan Ward-Smith and Chris Robshaw are also in as cover for Tom Croft and Joe Worsley, while scrum-half Ben Youngs fills in for Leicester team-mate Harry Ellis. England open their Six Nations campaign against Wales on 6 February.