Rodwell had a burgeoning reputation when he left boyhood club Everton to join Manchester City three years ago, before a string of niggling injuries prevented him from making a significant mark at the club.
Rodwell joined City for 12 million pounds but made only 16 league appearances in two difficult years and joined Sunderland before last season in a bid to jump start his career.
Further injuries and a loss of form, however, have limited him to only 20 league starts at Sunderland with his last six league appearances all coming off the substitutes' bench.
"Everyone is saying 'what's happened to Jack Rodwell?'," Sunderland boss Allardyce told reporters ahead of their home game against Watford on Saturday.
"It's clear the number of niggling injuries he's had and the two years at Manchester City have caused him to lose his focus and his confidence.
"I think we've got to rebuild that and the only way to rebuild it is to make sure we keep Jack fit and training every day and that when selected he hopefully finds that confidence again."
Rodwell, 24, came through the Everton youth system, and was a pivotal figure in then manager David Moyes's side when Manchester City came calling.
Yet with City already boasting high-profile midfield talent, Rodwell's career momentum was swiftly halted as he struggled for game time and failed to shine in his brief appearances.
When Sunderland paid 10 million pounds to lure him to the north east, it was widely expected that he would rediscover his lost form, but that has yet to materialise.
"Jack burst on to the scene with Everton at 17 years old but since he went to Manchester City he has not played as often as he would have liked and that was a big move that didn't pay off," Allardyce added.
Sunderland are second from bottom in the Premier League, but victory on Saturday would give Allardyce his fourth victory in eight league games since taking over from Dutchman Dick Advocaat in October.
"That would be a fantastic start for me," he said.
(Reporting by Toby Davis; editing by Ed Osmond)
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