West Ham will have been left to sweat over the severity of a knee injury to defender Fabian Balbuena following the Premier League defeat to Watford.
The Paraguayan, who has formed a firm partnership with fellow summer arrival Issa Diop at the back this season, limped off shortly after conceding a penalty with a poorly timed attempt at a challenge on Roberto Pererya, in which he picked up the problem.
Balbuena, 27, will be assessed at the club’s Rush Green training ground on Sunday.
West Ham have perhaps a more kind run over the festive period than some of their Premier League rivals. With Boxing Day off the Hammers face Southampton away on December 27 before travelling to Burnley on the Sunday, they won’t play after that until January 2 when Brighton visit the capital.
They may, though, have to navigate that run with just two fully fit central defenders with Winston Reid a long-term absentee, though Declan Rice could drop back from midfield and fill in.
Speaking after Watford brought the Hammers’ four game winning run to an end, Pellegrini said: “Fabian has a problem in his knee, we will see tomorrow what it is, I cannot answer that know what it will be.”
On the defeat, which sees the Hammers drop back into the bottom half of the table, Pellegrini added: “I think that we were a little bit unlucky to at least not get a draw out of this game. I think they had the penalty that was the only action that was inside our box in the first half. We had at least three or four chances to draw the game.
“When it is 1-1 it is different to play under pressure to get the win but we didn't get there. Unfortunately we didn't score and then they got the second.”
West Ham have won on just one of their last nine visits to Southampton, who are on a high after back to back wins under new manager Ralph Hasenhuttl.
