Cambridge United boss Jez George says they cannot afford to sign out-of-favour Brentford defender Michael Spillane at the present time.
The 22-year-old former Norwich man is currently training with the U's.
George told BBC Radio Cambridgeshire: "He's at a League One club so it's unrealistic for us to be thinking about bringing him in.
"But it's a good opportunity for us to have a look at him and for him to have a look at us."
Spillane, a former Ireland Under-21 international, knows George from his time in youth football. He has been deemed surplus to requirements at Griffin Park, but has been unable to secure a move away.
"I've known Mickey since he was a young lad and he got in contact to ask if he could come and train with us," George said.
"A couple of loan moves have broken down for him and we're always keen to look at good players."
Meanwhile, defender James Jennings has returned to training after missing Saturday's win at Mansfield. He was taken to hospital after feeling unwell on Friday night.
"We were really worried about James at the weekend as he was really struggling and they weren't too sure about the problem," George said.
"Fortunately it seems to be settling down. It's always worse when it's not a football injury as such."