Jamie Vardy is a doubt for England's World Cup quarter-final against Sweden with a groin strain.
The 31-year-old made an impressive impact as an 88th-minute substitute in the last-16 clash against Colombia on Tuesday but was conspicuous by his absence from the five spot-kick takers.
However, PA Sport understands the Leicester striker sustained a groin complaint.
Vardy had an injection after the match and will now be sweating for his place in Saturday's quarter-final against the Swedes in Samara.
Southgate said that the dressing room was "like a scene from M*A*S*H" after going the distance in Moscow, where Dele Alli, Ashley Young and Kyle Walker were others that looked in discomfort.
The England manager expects to get a clearer idea about the severity of any issues by Thursday, when the team will hold a training session behind closed doors.
Only eight players trained in the pouring rain at Spartak Zelenogorsk on Wednesday, having only returned to their Repino base at around 6.30am.
Marcus Rashford was the only player to feature against Colombia among the playing group which was outnumbered by staff.
The 20-year-old forward was brought on late in extra time and was not deemed to have done enough to warrant a normal recovery session, which the other players did back at the team hotel.
Fabian Delph has yet to return to camp after heading home for the birth of his third child after the final Group G match against Belgium last Thursday.
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Meanwhile, Harry Maguire insists England showed they are "fearless" against the South Americans.
The Three Lions looked to be heading through in normal time against following Harry Kane's penalty, only for Yerry Mina to equalise in stoppage time.
The tie was eventually settled from the spot, England winning their first-ever World Cup penalty shoot-out.
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Next up for Gareth Southgate's side is a last-eight clash with Sweden in Samara with Maguire insisting the squad - which was the most inexperienced of all 32 nations at the start of the tournament in terms of international caps - is mentally strong enough to cope with any challenge.
"We have shown against Colombia that we are hungry, we are fearless. The boys showed great character," the Leicester defender told the London Evening Standard.
"There have been a lot of questions about us about how we are a young team and that we don't have much experience."
Colombia collected six yellow cards on the night and were roundly criticised for their heavy-handed tactics.
But to Maguire, coping with such issues is just further proof that the current team can do what needs to be done - even in trying circumstances.
"There were some things going on out there that I have never seen before. It was a bit crazy at times," he added.
"We conceded in the 93rd minute when we were fully in control and were really comfortable - the only way they were going to score was from a set play.
"It was a great ball, a great header and something we will have to look at and try and improve on. But to come back and still win the game is really promising."
