A triple set of blows hit Manchester United on Saturday as striker Romelu Lukaku was stretchered off at Old Trafford after a clash of heads.
Then Manchester United drew 0-0 with Southampton losing two vital points and their second position in the Premier League.
Chelsea, the defending champions who played earlier and crushed Stoke City 5-0 are now second on the table, displacing United, by a point.
Lukaku crashed into Southampton’s Wesley Hoedt as the pair contested an aerial challenge early in the first half at Old Trafford.
The Belgium striker lay prone on the pitch barely moving while he was treated by medical staff for five minutes.
Lukaku remained conscious and was eventually carried off wearing an oxygen mask.
The injury continued a difficult period for Lukaku, who has scored just four times in his last 19 appearances for Jose Mourinho’s side.
In the absence of Lukaku, Mourinho’s men were unable to break down Southampton and had to settle for their third successive league draw.
Man Utd had penalty claims turned down and Jesse Lingard headed narrowly wide.
In the second half, Saints striker Shane Long nearly was superbly denied by the outrstretched leg of David De Gea.
Paul Pogba had a goal disallowed for offside late on, as Alex McCarthy, replacing Fraser Forster in goal for Southampton, held firm to keep a clean sheet.
United ended a frustrating December trailing 14 points behind leaders Manchester City, who face Crystal Palace on Sunday.
“When you see a player leave the pitch like he did, it is usually two games at least,” Mourinho said of Lukaku.
“We missed easy chances but I’m really unhappy because we should have had a penalty.”