The 38-year-old shot-stopper will be between the sticks for Town tomorrow with regular No.1 Max O’Leary not permitted to play against parent club Bristol City.
Murphy has made eight appearances for Shrewsbury – two in League One – since joining on a free transfer from Bury in the summer.
It has also been reported in Bristol that the Robins are considering recalling O'Leary, 23, to become their homegrown club developed player for the remainder of the season.
Ricketts, who confirmed the struggling Championship Robins had denied O’Leary permission to play, said of Murphy: "It's nothing he's not done before.
"It's funny, as a keeper he's sat on the bench for the majority of the season but has played half-a-dozen games and done very well in those.
"Now he gets the opportunity in the biggest Cup competition in the world away from home against a really good Championship side.
"(That experience) was a lot of the thinking behind why we went and got the mix with the keepers, either way they are young, up-and-coming or experienced with good know-how so both have an advantage and feed off each other."
Asked if the Irish shot-stopper is fighting for a first-team place in future games Ricketts said: "I think that's the way in any position. You can only do your best and try to make it as hard as possible for me who picks the team."
Murphy starred on his league debut, crucially saving a penalty in the victory over Peterborough, before an error was capitalised on by Bristol Rovers in the Gas’ 4-3 win at Montgomery Waters Meadow.
Lee Johnson’s side have lost five of their last six games and could rotate their squad for tomorrow’s third round tie at Ashton Gate.