The Rovers boss was disappointed by the performances of his substitutes in the final pre-season friendly against Harrogate Town.
With a small squad and multiple key injuries, Wellens says everyone is close to featuring in his starting XI and must show they are worthy of a place.
“We’ve given the opportunity to Charlie Seaman and Branden Horton and others, and they want to go through the motions,” Wellens told the Free Press. “We won’t accept that.
“If you get 20 minutes you’ve got 20 minutes for a reason - it’s to bring the game back to our way, to give us energy and some aggression.
“They’re part of the first team squad.
“At the moment, we are very short in midfield and we might need to start Branden Horton at left back. But Tommy Rowe was excellent at left back again as you’ve seen.
“I wanted the subs to come on and show me some real intensity.”
Wellens admits he felt some sympathy for centre half Cameron John who was left on the bench throughout the Harrogate game.
John has impressed through pre-season and will be given 90 minutes in Wednesday’s behind-closed-doors friendly with Watford at St George’s Park.
“I wanted to play my two centre halves to play 90 minutes because I want that cohesion,” he said.
“But you’ve got Cameron John who is a fantastic lad with a great attitude, who trains every single day and has had a brilliant pre-season. Because Ro-Shaun Williams and Tom Anderson have done very well as well, it is difficult to get him minutes.
“I don’t see him as a left back, I see him as a centre half and it means we’ve got three really good centre halves.
“He’ll be beating himself up on the way home because he didn’t get any minutes.
“He’ll play 90 minutes in that game. But he’s sat there devastated because he’s not got on the pitch.”