SAINTS centre Mark Percival is seeing a specialist to determine the next move in treating the troublesome hamstring injury that forced him off the pitch during Saturday's Challenge Cup tie.

Although the England international had "ticked every box" presented to him by the club's staff during his recovery from the injury aggravated in the Castleford game in mid August, the reoccurance has left Saints seeking further answers.

Percival's departure, midway through the first half, was hugely damaging with Saints not simply losing a top-drawer strike centre, but were also forced to reshuffle their back row and limit their effective interchanges.

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Saints coach Kristian Woolf explained that the club's medical staff had not taken any risks in playing him, having jumped through all the hoops in rehab and in training before being selected.

Saturday's blow, sadly, sends them back to square one.

Woolf said: "It is frustrating for everyone, none more so than Mark himself. He is a competitor who wants to be out on the field and helping his teammates. He is an outstanding player.

"I don’t think there’s a better centre in our competition than him. He certainly showed his class in that first 15-20 minutes and if he stays on the field then he goes a long way to making that a different result as well. That is how much influence he has.

"It is really frustrating for him and for everyone.

"We now have to get that injury scanned and looked at by some specialists to figure out exactly what is going on and make sure that what we do next we are not putting him in that same boat."

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Percival was initially left out of Saints' second game since the restart as a precaution due to a tight hamstring, but then departed early in the game at home to Castleford, which forced him out for the next month.

Woolf explained: "I know our staff had ticked every box and done everything right – and if anything had been over cautious because he could have played the week or two before if we wanted to push it.

"Every box – from the scans, knowing what the injury is, daily treatment, daily rehab, the machines we have access to to help with recovery and muscle repair, his re-introduction to running and him getting the strength and endurance work that needs to go into muscles to make it ready for competition - was ticked.

"We had done all of that and given it some time to make sure it was beyond good.

"He had passed every test before that game, there was nothing he or our staff could have done more.

"Now we need to get to the bottom of why this keeps happening.

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"He is now under a specialist in that area and we are not quite sure what the results are going to be, the scans and the causes of the problem, then we treat it from there."

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It is highly likely that teenager Josh Simm will step back into Percival's boots for Tuesday's game against Wigan.

Woolf also gave an update on Jack Welsby, another first half casualty in the Warrington cup tie, and the news is positive.

"Jack copped a heavy head knock towards the end of the first half which meant he was ruled out for the for the game," Woolf said.

"He is fine now, but it was the right call for him to not continue playing.

"He recovered the next day and will be right for the next game as well.

"To lose two outside backs in the first half of a game puts a lot of pressure on a team."