Rooney and Bertrand were the only players absent from training at Tottenham Hotspur's north London training base
Rooney and Bertrand were the only players absent from training at Tottenham Hotspur's north London training base on the eve of Tuesday's meeting with Spain at Wembley.
Rooney returned to England's starting XI for Friday's 3-0 win over Scotland in World Cup qualifying, having started the previous game -- a 0-0 draw away to Slovenia -- on the bench.
"Both are being assessed. They had minor issues this morning so we'll have a look at them as the game goes on," Southgate told his pre-match press conference at the Tottenham training ground.
"Obviously they weren't able to train so they must be a doubt, but until we look at them we won't know for sure."
Southgate said Rooney will not start the game in any case and confirmed Liverpool midfielder Jordan Henderson will fill in as captain.
Harry Kane has already been ruled out of Tuesday's match, the Tottenham striker having returned to his club as he continues his recovery from an ankle ligament problem.
The game against Spain is the fourth and final match of Southgate's tenure as interim manager, but he is expected to be offered the role full-time.