After being flattered and praised by a host of interested managers throughout May and June, Lee Johnson's criticism of his game was what convinced Alfie Mawson to choose Barnsley.

The 21-year-old centre-back – who was nominated for League Two Player of the Year last season after impressing on loan at Wycombe – had been one of the most in-demand free agents since rejecting a new contract at Championship parent club Brentford.

Mawson was shocked when Reds' head coach Johnson told him the weaknesses in his game while attempting to bring him to Oakwell but admits honesty was key.

"I talked to quite a few managers and had good conversations but the thing that swung it Barnsley's way massively was the fine details in what the manager said to me," Mawson told the Chronicle.

"He didn't just tell me I had done well. He told me what my weaknesses were and how he could improve me. He told me that I have to work on my defending in my own box from crosses. To be honest, I was blown away by that. It hit me and I knew it was exactly what I needed to be hearing and completely different to what everyone else had been saying. He went about it in a nice way and he was right. It's nice to be picked up on that.

"He went through weekly schedules of how he will work with me in training.  I think that, under his guidance, I will improve the best and the quickest."

Johnson is confident he can improve the centre-back and said his method of spelling out a potential signing's strengths and weaknesses when meeting them will be followed up after they sign. The Reds head coach told the Chronicle: "It's not a tactic like a car salesman would use, it's a genuine belief that we can make the player better.  We've shown that with players like Conor Hourihane and George Smith.

"Alfie is a big signing for us and he looks the part already in training.  He's a big strong lad. It was a big boost for us to get him to Barnsley because there was a lot of other interest in him but he's not the finished article.  With all due respect to Wycombe Wanderers and League Two, this season will be a big step up for him. "But we are confident that he will continue to improve and be a really good signing for us."

Mawson will add to a centre-back department that already includes Lewin Nyatanga, the most experienced outfielder at the club who recently signed a new deal, summer signing Marc Roberts and highly-rated academy products Mason Holgate and Jack Cowgill.

Johnson said: "I am happy with the centre-backs at the club and I won't be looking to bring any more in now.  I always thought it would take three transfer windows to get the squad that we want in all positions but I think we are already there with centre-backs."

Johnson hopes that Mawson's recruitment will convince other players to choose Barnsley. He said: "It's no secret that we are going for young, talented, mobile players and Alfie certainly fits into that. Signing him is a statement of intent and hopefully it will make some of our other targets realise what we are trying to build here."

Mawson signed a three-year deal at Oakwell and Barnsley and Brentford are currently negotiating a compensation fee, as he is under 24, with the Reds not expecting the case to go to tribunal. The defender never played a league game for Brentford and was also loaned to Luton, Welling and Maidenhead.