Essentially he's a little bit like Glen Johnson, he's an ultra attacking full back who simply goes further forward more often and as such looks like he gets a lot of attacking work done but like Glen Johnson, leaves huge holes at the back, is constantly out of position and isn't that good.
He went to Benfica, ended up on loan because he was basically a pretty weak ass winger/attacker, they shoved him in defence where he had that "fullback who scores or assists a few, must be brilliant" moment, while people ignored he was crap in defence. He somehow moved for 30mil, he had an entire 12 starts in the league first season 16 starts in the league last season... 3 assists that first season 1 goal 1 assist the second, 5 yellows that first season, 2 yellows 1 red this season in a fairly small number of games(and being VERy lucky not to get more both seasons). Not a goal or assist in any Champs league game in two seasons(he played quite consistently in the champs league compared to the league). Now that would be fine if he was a defensive fullback who didn't get forward much in a low scoring team who couldn't convert chances, but he's an ultra attacking fullback who can't defend, with at least two brilliant finishers to provide to and he did squat in two years.
He only had 23 starts and 2 goals for Benfica when Mourinho decided to waste 30mil on. Like Marcelo and Johnson, every now and then they'll have a game where they bomb up the wing, score a goal, get an assist and don't screw up too badly defensively. Most games they bomb up the wing, lose the ball, try a stupid shot, dive a bit, run back after losing the ball and do something worthy of a red card.
He's fast and strong, which like Marcelo occassionally leads to a lucky game but no footballing brain at all and bad tempers. The very few goals/assists he has have been against Luxemberg, Israel, Azabarubbish for Portugal, Levante, Ossasuna, Espanyol and Valencia(in a 5-0 drubbing by the team).
Most of Spain thinks Mourinho bought him because he was Portuguese and not much else(like several other flops he's bought for seemingly that reason alone), the club, fans, pundits, no one thinks he's good enough to stay. But he's had a big money move and big wages... a smaller club would be mad to take him on.
Honestly while Real love Varane, for such a high fee if you were to lose Bale anyway I'd leverage that into nabbing Varane, not least because if he wants out in a few years he'll go for a crapload. Varane looks like the real deal. If they want Bale THAT badly you leverage a player off them they DON'T want to lose, not help them offload their biggest waste of space
You may be able to nab Benzema, who would be worthwhile for you as well.... the problem being he's a more recent buy where big wages went with big transfers so Benzema could easily be on a stupidly big wage.