O’Neill noted that the former Nigeria skipper is now in tip-top condition and lauded that the central midfielder for staying humble player despite winning several titles during his time with Chelsea.
Mikel could captain the Potters for the second game in a row with Sam Clucas rated as doubtful to face the Bees due to a calf issue.
The 33-year-old has gone the distance in each of the last six matches played by Stoke City in the Championship and claimed an assist in the 1-0 win at Preston North End.
“John’s been good and I think with every game he gets better. We knew it would take him a bit of time having not played since March. He was not going to come in and be straight up to speed,” O’Neill was quoted as saying by StokeonTrentLive.
“But I think he has done exceptionally well to get through 90 minutes as often as he has done and I think with each 90 minutes we see an improvement in his level of performance.
“I think you can see what he brings to the team with that physical presence and quality on the ball as well.
“Particularly against Barnsley we started to see some great play and real intricate passing from him as well.
“He does a great job for the team, John. He has a great tactical knowledge and he is a real help for the players around him as well.”
He continued : “I think John is (up to speed) now. He has a style of play that sometimes makes it look like he’s off the pace but that’s not the case when you reanalyse the game.
“He’s just very economical in how he plays and more importantly he’s very efficient with his use of the ball.
“We’re delighted with what he’s brought to the team.
“When we brought him up here and spoke to him about coming to the club he was very positive and the good thing about it that he has been what he said he would be.
“He’s fitted in extremely well with the group of players we have. He was at Chelsea and won everything in the game but he has great humility and he’s a big plus for the squad.”
Mikel spent ten and a half years with Chelsea and won the Premier League twice, the FA Cup four times, the League Cup twice, and the Champions League and Europa League prior to his departure.