Walker will join the Sixways club following the arrival of Carlos Spencer, who joined the Kingsholm club last week on a 17-month contract.
He has made 17 appearances in all competitions this season and has scored tries against Bath in the Guinness Premiership and Wasps in the EDF Energy Cup.
Since he made his debut in 2006, Walker has made 64 appearances and has scored six tries.
"Willie is an outstanding professional and has made a significant contribution to us this season," said head coach Dean Ryan.
"He is versatile enough to be deployed in a number of positions and has been a valuable asset to the club since he joined three seasons ago.
"But the arrival of Carlos Spencer is likely to restrict his opportunities in the coming weeks and for that reason we feel it is prudent to look at this loan arrangement until the end of the season, where I am sure he will be a success at Worcester."
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