Former Great Britain rugby league star Andy Farrell is to have an operation on his back on Monday and could be out of action for a further three months.
The 30-year-old is suffering from a prolapsed disc in his lower back as a result of a car accident.
Farrell is still waiting to make his rugby union debut six months after joining Saracens having been sidelined by a broken toe since August.
He could be ruled out until mid-March and may struggle to play this season.
Farrell, who switched codes in a £700,000 move from Wigan in March, was set to make his debut in Saracens' Heineken Cup match against Ulster before being involved in the road accident last week.
Initially the incident caused no distress but his back stiffened up and scans diagnosed a prolapsed disc.
Saracens chief executive Mark Sinderberry said: "It's terrible luck for Andy - particularly as this injury hasn't been picked on the rugby field.
"In a year in which Andy has suffered some very bad luck, this is a cruel blow to suffer such an injury away from the pitch - especially coming when he was nearing a return to full fitness."
Coach Steve Diamond revealed on Saturday that Farrell was "depressed" by the wait.
"We value Andy immensely. He's a proud man and a leader of men so he's depressed by the situation.
"When he's fit we're confident he will make a huge impact."
His entrance into the 15-man code, whenever it occurs, will be watched with interest by England coach Andy Robinson, who named Farrell in his Elite Player Squad before he had even played a game of union.
Farrell is expected to play at inside centre, with a possible switch to the back row pencilled in in the longer-term.