Southgate confirmed there were no major injury concerns, but would assess Manchester United forward Rashford ahead of the first scheduled open training session on Wednesday.
Rashford, who scored 13 goals in all competitions for Manchester United this season, is battling for a starting spot against Tunisia and strengthened his case with a goal in the 2-0 friendly win over Costa Rica on Thursday at Elland Road.
England touched down in Russian Federation on Tuesday and upon their arrival, Southgate revealed that the 20-year-old had an issue with his knee and is now being assessed by the Three Lions medical staff.More news: British PM fends off Brexit parliamentary defeat
"He doesn't really like to be overloaded in midfield so, if he does see that, then I tuck in so we go as a back three".
England face Tunisia in their opening Group G fixture on Monday, before taking on Panama and Belgium.
"We are obviously excited to be here now".
"It is a World Cup - there is always going to be pressure, nerves and excitement".More news: Nadal has no 'obsession' to hunt down Federer tally
"Knowing the manager and having worked with him before, I know what he's like and i'm pretty confident as long as I keep my feet on the ground and working hard I'll get my opportunity".
England's arrival at their hotel was met with a strong security and media presence.
The displays in the warm-up matches have been in contrast to England's performances in recent years, which critics say have been hallmarked by disjointed and often tiresome football - just 40,000 fans turned up for a friendly against Norway at Wembley in 2014, and some travelling fans booed a the end of a 4-0 win in Malta last year.
Early exits in the group stages at the 2014 World Cup and in humiliating fashion to Iceland at Euro 2016 have tempered expectations England can end a 52-year wait to win the World Cup. "We want to take this tournament head on".More news: Montreal expected to host World Cup games in 2026