Tranmere boss Rob Edwards has admitted concern over Liam Ridehalgh's ankle injury has forced the club to step up its search for cover at full-back.
The extent of the 23-year-old's injury remains unclear, but he will miss Tuesday's friendly against Everton.
"The squad is thin at the back - defensively and the left side are very thin. We need to get more players in," Edwards told BBC Radio Merseyside.
"Now with Liam out, it is an absolute necessity that we do that."
The 41-year-old former Exeter City assistant manager continued: "It looks a little bit like it might be more than a couple of days [that Ridehalgh is sidelined], which is a worry for us as we only have one left-back at the club."
Ridehalgh, who was injured in Friday's pre-season match at Rhyl and ruled out of Saturday's loss against non-league Marine, made 38 appearances for Tranmere last term, having initially joined the then League One club on loan from Huddersfield Town.