Joselu says Mark Hughes gave him "no chance" to succeed at Stoke City.
The striker joined Newcastle United last month in a £5million deal.
And Joselu – who has made a positive start to his career on Tyneside – will face his former club at St James's Park this afternoon (3pm kick-off).
The 27-year-old says he had to leave Stoke because of manager Hughes, who loaned him to Deportivo La Coruna last season.
"I had no chance," Joselu told the Daily Mail. "I scored goals, I played well, but the manager did not give me a run of games.
"He (Hughes) is the reason I’m not there. He didn’t trust me. Now I have a manager (Rafa Benitez) who does. When I had the offer to come, it was the only place I wanted to be."
Hughes has also had his say on Joselu's departure from the Britannia Stadium.
“Joselu wanted to go – he didn’t want to be here anymore," he said. “In his first year, he felt he didn’t get enough opportunities.
"Saying that, I think he made about 22 appearances for us. Those were substitutes and starts as well.
“I think in terms of what the other strikers had, he had a decent stab at it, but he came in after the first season and said he didn’t want to be in Stoke and that’s why we allowed him to go out on loan last year.
“He came back and we thought 'let’s see where we are with him' – but the first knock on the door was Joselu saying he didn’t really want to be here and wanted to leave.
“He had a decent pre-season, but maybe that was with a view to moving elsewhere. Maybe that’s why it was as good as it was.
“He has moved on and we have moved on, he seems to have settled there and he is getting regular game time, which I didn’t feel I could give him, so we will see how he goes.
“I’m sure he’ll want to do well against us. He was a good player and we brought him here with the intention of him playing more.
“He had some good games and affected games in a good way – technically he's a very good player – but he was never really able to have a run of performances that enabled him to hold on to the shirt for long enough.
“That’s how it goes and I think he maybe could have given it a bit longer than he did, as we saw his quality and we rated him.
“I just felt he wanted to be playing week in, week out and we weren’t able to give him that – it is what it is.
“We got our money back and maybe people will think we should have got more because of the inflated market, but he was agitating to go, so in the end we got our money back and moved on.”
Meanwhile, United manager Rafa Benitez is looking to "improve" Joselu, who scored on his full debut at St James's Park late last month.
“Normally if a player has played for a team, they score against their former team," said Benitez.
"We knew him as a player and he is showing what we knew about him. Now, it is about him remaining consistent and improving. He has plenty of room for improvement, but we are happy with him."