Roberto Mancini is concerned that Manchester City's summer transfer strategy that ended in a rush to sign players at the last minute may have caused the stuttering start to their title defence.

City are four points behind the leaders Chelsea, who have 13, and have conceded 10 goals in all competitions – seven in the Premier League, three in the Champions League.

In the opening group game at Real Madrid last Tuesday two late goals saw a 2-1 lead game to end in defeat. This was followed by Laurent Koscielny's 82nd-minute equaliser for Arsenal in the 1-1 draw at the Etihad on Sunday.

In the closing 24 hours of the transfer window Manchester City signed Internazionale's Maicon for £4m, Swansea City's Scott Sinclair for £6.2m, Benfica's Javi García for £15.8m and Matija Nastasic from Fiorentina for £12m (including Stefan Savic as a makeweight). Mancini also recruited Richard Wright on a free transfer as the third-choice goalkeeper. Only the £12m deal for Jack Rodwell was completed in early August.

Yet at the start of the summer Mancini targeted Robin van Persie, who went to Manchester United for £24m, Roma's Daniele De Rossi, valued at £30m but who stayed at the club, Eden Hazard, bought instead by Chelsea for £32m, and Javi Martínez, who cost Bayern Munich £32m.

Asked if the introduction of new players had been a factor after seeing Arsenal fight back, Mancini told the Manchester Evening News: "It could be this. We had new players only in the last two or three days of the market and maybe these players don't know their team-mates well and need time."

James Milner is to see a specialist to assess how serious his toe problem is. The midfielder, who missed the draw against Arsenal, was not included in the 18-man squad at Real Madrid and has started only one match this season, the 2-2 draw at Liverpool in late August.

Mancini added: "Milner has a problem in his toe. He has pain. He will see a specialist and after that we'll decide what to do."

Maicon was also absent against Arsenal having suffered a foot injury against Madrid and will miss Tuesday's League Cup visit of Aston Villa.