Grant and Martins Indi are currently on loan at Stoke from Derby County and Porto respectively but the club are expected to enter talks with the pair in the coming weeks, in a bid to sign them full-time when the January transfer window opens.
Pieters feels the duo have settled in well with the Potters and hopes both players agree permanent deals with the club.
"I will be happy for that and for them," Pieters told the Stoke Sentinel. "They have shown they can be a real value to Stoke.
"You guys are maybe surprised by Bruno, but I saw him playing in the Dutch league and saw him playing a couple of times at Porto and with the national team, so for me it's not a surprise.
"I'm happy he's going to play games again and is standing next to me. He is playing a good couple of games and it's now for him to develop his play to make sure he is number one in the position, and is getting better and better every week."