Saido Berahino must be mentally focused on performing for West Brom to return to his best form for the club, according to Tony Pulis.
Berahino started Saturday's 1-0 Premier League defeat at Bournemouth as a lone striker and almost gave West Brom the lead early in the second half when the game was still goalless, but was withdrawn for Salomon Rondon after 63 minutes.
A late Callum Wilson winner condemned the Baggies to their second defeat of the season, and Pulis says his tenure in charge of the club has been made harder by Berahino constantly being linked with a move away.
The 23-year-old remained at West Brom after the transfer window closed despite heavy interest from Stoke City.
"For over a season Saido has been wrapped up in where he's going and he's playing in the top league in the world. You have to be mentally prepared, you can't just switch it on and off and he needs to understand that," Pulis told BBC Sport.
"In the 20 months I've been here he was a talisman for the first six months but then we've lost him for the last year. It's been difficult.
"It's been an interesting club to manage for me, the way it's run is different, but also dealing with a player that has for two thirds of that period not doing really what he should be has been difficult."
Pulis was pleased with the contribution of record signing Nacer Chadli, who made his debut for the Baggies in the defeat.
"He's a good footballer. His movement is fantastic. He passes the ball really well. It's a pleasure to watch him play," Pulis told the club's official website.
"We've got to try and get him the ball more at times. There were opportunities to give the pass today, and we've gone out and gone the other side. He's a player, I'm sure, who will make and score us goals."