Billy Vunipola could miss Saracens' Champions Cup quarter-final against Leinster after director of rugby Mark McCall revealed his fitness remains shrouded in doubt.
The England number eight fractured his arm in January, missing the Six Nations as a result, and was pencilled in to return in time for the trip to Dublin on April 1.
It was the latest setback of torrid 18-month spell that also included substantial lay-offs due to knee and shoulder surgery and McCall will not gamble on his fitness against Leinster.
“It’s a little bit uncertain, Billy is in a race against time to be ready for the quarter-final,” McCall said.
“We’ll make a call on what the surgeon says. If the arm isn’t right to play then we won’t risk him. He’s been injured enough, we don’t want to re-injure him.
“Billy is very close to coming back but whether he makes the quarter-final we’re not sure yet.”
Vunipola’s comeback is being monitored carefully by England, who sorely missed the rampaging back row during their fifth place finish in the Six Nations that was sealed by a 24-15 defeat to Ireland on Saturday.
Nathan Hughes filled the 25-year-old's boots for two matches only to suffer a knee injury that required surgery, while Sam Simmonds started three games only for concern to be raised over his size for a number eight.
If fit, Vunipola will be an automatic selection during the three-Test tour of South Africa that takes places in June.
Saracens name their team for Saturday’s Aviva Premiership clash with Harlequins at the Olympic Stadium on Friday.