The 25-year-old seemed on course to be the Bucks’ No.1 before the start of the season but Leicester loanee Max Bramley has been first choice.
Andy Wycherley came in too and, due to an injury, Martinez ended up behind him in the pecking order.
Cowan was firmly of the belief he needed to get minutes under his belt and, explaining the decision to let him depart the club rather than go out on loan, the Telford chief said: “Our budget will be one of the bottom five in the league, we have to remember that.
“Ultimately, having three keepers just isn’t feasible.
“With Shez, we’ve got to be cruel to be kind. He needs to play games.
“He could easily be our No.1 but he picked up an injury and we’ve got two other very good goalkeepers in Max and Andy. It’s just been unfortunate for him.”
Martinez re-joined Telford in the summer after a spell last campaign in which he did not play at all.
He made two appearances for the Bucks this term – the 1-1 draw at Guiseley and the 2-1 victory over Brackley Town, dislocating one of his fingers in the latter.
And Cowan has backed Martinez to emphatically respond to this setback.
“Shez has been fantastic for us. His attitude has been excellent, he’s been a credit to himself,” he said.
“He just needs to play football and this is the chance for him to do that.
“I wouldn’t be surprised to see Shez go out and prove himself, and come back. He’s proved he’s good enough for this level so the door is certainly not closed on him.
“If he goes anywhere, I’d like him not to sign a contract. An opportunity could come up again for him here.”
Telford have also cut Dan McKenna’s loan spell from Wolves short.
The midfielder was due to stay with the Bucks until January but has returned to Compton after failing to make an appearance.
“He’s another fantastic young man. He came in and worked really hard,” added Cowan.
“He just couldn’t get near the squad because of the form we’ve been in.
“We’re not in the business of killing careers, harming the development of a young player.
“He needs to go back to an amazing environment at Wolves and continue to be nurtured.”