It says a lot for how badly things have panned out this season for Swansea and West Bromwich Albion that when they meet at the Liberty Stadium on Saturday with their minds beset by relegation worries, both clubs may choose to omit the signings about whom they were most excited in the summer. For Swansea and West Brom to attract talents of the pedigree of Renato Sanches and Grzegorz Krychowiak was a coup but so far both midfielders have been spectacular flops.

Rather than reignite their careers by leading their clubs to a higher level, each has sunk to personal nadirs, losing their places as their teams have tumbled down the league. Club and player alike must be wondering whether they have made terrible mistakes.

Both players came to the Premier League on loan from leading European clubs – Sanches from Bayern Munich and Krychowiak from Paris Saint-Germain – and both hoped to use their secondments to prove, after periods of relative inactivity at their parent clubs, that they remain elite players. The evidence so far suggests the contrary, although it is too soon to draw a conclusion, especially in the case of Sanches, who is 20 years old.

Beyond the similarities there are differences in the players’ cases. Krychowiak, seven years older than Sanches, arrived at West Brom with a visible conviction that he would live up to his billing. He was not at peak sharpness, which was natural considering how infrequently he had played for PSG, but there was no sign his morale had been damaged by his alienation by Unai Emery, the manager who had been so eager to bring him to France after winning two Europa Leagues with him at Sevilla. A few months after signing the Pole for £34m Emery complained the player was unable to handle the higher level at PSG.

On his debut for West Brom, away at Brighton in September, Krychowiak looked confident. He was assertive vocally and with the ball, shouting instructions to team-mates – and, at one point, loudly rebuking Allan Nyom for not making a particular run. One exquisite 40-yard pass might have led to the game’s opening goal if Matt Phillips had not miscontrolled it. Krychowiak faded in the second half – and not only, perhaps, because of a lack of fitness: West Brom’s negativity gradually seemed to wear him down.

For PSG, Sevilla and Poland, Krychowiak played an attacking style in which his team had a lot of possession and abundant passing options. West Brom, by contrast, have had the lowest average possession of any team in the Premier League this season (37.7%). Under Tony Pulis, Krychowiak was often deployed in a deep three-man central midfield and found that when he got the ball he had fewer opportunities to pass forward. At Brighton he attempted 59 passes, a tally he has not reached in any of his nine subsequent Premier League appearancessince. It looked as if he became disenchanted on realising he had chosen unwisely, joining a team who did not play to his strengths.

Renato Sanches must wonder about the situation he walked into, just as Swansea must wonder what has become of the player who, in 2016, won the Golden Boy award. Photograph: James Marsh/JBPI/Rex/Shutterstock

Pulis, like Emery, appeared to conclude the player did not do enough to assert those strengths. It was telling that one of Pulis’s last acts as the West Brom manager was to replace Krychowiak with Claudio Yacob at half-time during the 4-0 home defeat by Chelsea. Pulis had an idea he was going to be sacked after that match and seemed to decide if he was to go down, he would at least do it with people who he knew would fight for him. Off came Krychowiak.

After Pulis left, the caretaker manager, Gary Megson, introduced Sam Field instead of Krychowiak, hailing the 19-year-old as the finest passer at the club. Field performed so well that the new permanent manager, Alan Pardew, stuck with him. So in West Brom’s last match, against Crystal Palace, Krychowiak sat on the bench while Jake Livermore was joined in midfield by Field and the 36-year-old Gareth Barry. Pardew will play more adventurously than Pulis but Krychowiak cannot expect to walk back into the side. His environment may have changed for the better but he needs to rediscover his dynamism.

Sanches must also wonder about the environment he walked into, just as Swansea must wonder what has become of the player who, in 2016, won the Golden Boy award for the most promising youngster in European football, a prize previously won by Lionel Messi, Cesc Fàbregas and Paul Pogba. Swansea’s manager, Paul Clement, worked with Sanches at Bayern but may have underestimated the extent to which the player’s confidence has been shattered by his failure to make the grade in Germany. Sanches’s performance at Swansea has been downright sad.

He looks meek and broken, unable to show the power, finesse and anticipation that led Bayern to sign him after seeing him dominate, as an 18-year-old, a Champions League duel against a midfield featuring Xabi Alonso, Thiago Alcântara and Arturo Vidal. The highlight of his time at Swansea has been the unintentional pass to an advertising board during the recent defeat at Chelsea.

Sanches has not been helped by the fact Swansea’s other transfer activity was so garbled he has occasionally been asked to fill the playmaker void left by the failure to replace Gylfi Sigurdsson. But nor has he been able to fill the gap left by Jack Cork, now revelling at Burnley. Clement has vowed to pursue excavations for Sanches’s buried potential but, after the display at Chelsea, he had little choice but to drop him for the defeat at Stoke. Starting Sanches against West Brom would be a declaration of extreme optimism. Or desperation.