Alli has joined the Turkish giants from Everton until the end of the season, with the option to make the move permanent.
The 26-year-old only joined the Toffees from Tottenham Hotspurs on a two-and-a-half year deal in January but could not rekindle his old form, making just one start in his 13 appearances for the club.
Once the darling boy of English football, Alli's stock has fallen remarkably in recent years.
The two-time PFA Young Player of the year joined Spurs from MK Dons in the summer of 2015 and impressed particularly in his first two seasons at the club, reaching double figures for goals in both campaigns.
His form dropped off in the last two seasons and he struggled for game time under Jose Mourinho, Nuno Esperito Santo and Antonio Conte before joining Everton in January.
Having helped England reach the semi-finals of the World Cup in Russia four years ago, few would have predicted that Alli would not be on the plane for the next tournament but that is the start reality he faces after moving to Turkey, according to Bent.
“He’s not getting back into the England World Cup squad, don’t care what he does between now and then,” Bent said on Drivetime.
“I would’ve liked to have seen him stay at Everton, work hard and try and get himself in the team.
“I think when you take yourself to Turkey that spells the beginning of the end. Finished.
“Going to a big club like Everton, playing under Frank Lampard who he can be compared to in terms of scoring goals from midfield, I though that would’ve got him firing. That didn’t work.
“He’s going to Turkey, Gareth Southgate’s not going to watch the games, that door’s closed.
“But maybe for Dele Alli that takes the pressure off, although there is pressure to play for a big side like Besiktas as fans can turn on you very quickly, it takes him out of the limelight in England.
“I feel a bit sorry for Dele Alli. From where he was to now, sad.”
