The Real Madrid winger did not start in Los Blancos' Champions League triumph on Saturday night, fueling speculation he could be on his way out of the Bernabeu.
And Collymore claims that United boss Jose Mourinho should use Real target David De Gea as leverage in a deal for Bale.
"Manchester United in particular would be able to match — even better — his income were they to sign him, and there are no guarantees he will play week in, week out if he stays in Spain," Collymore said in The Mirror.
"And I'd be using the fact David De Gea is a live target for Real to the best of my advantage.
"Don't get me wrong, I'm not saying Bale would be any sort of makeweight — he's too big a deal himself for that.
"But Real's hopes of landing the Spain goalkeeper might just give Mourinho some wiggle room to make a counter bid and, with Isco's form, Los Blancos might just consider it."