Arsene Wenger’s side moved to within two points of leaders Leicester City after a 2-1 win against the Foxes at the Emirates Stadium on Sunday afternoon.
Cech has been ever-present in Wenger’s first-team since the 33-year-old Czech Republic international swapped Chelsea for Arsenal last summer.
Speaking to Sky Sports on Thursday morning, former Arsenal midfielder Merson emphasised the importance of Cech to Arsenal’s title bid this season.
“If Arsenal win the title, it’ll be down to Cech,” Merson said.
“He has saved them points this season. Welbeck was a big bonus him coming back and scoring. There is so long to go [in the title race].”
Arsenal are in third place in the Premier League table behind Tottenham Hotspur and Leicester.
The Gunners host Hull City in the FA Cup fifth round at the Emirates Stadium on Saturday in a repeat of their 2014 final win at Wembley.
Arsenal’s next Premier League game is a trip to bitter rivals Manchester United at Old Trafford on Sunday 28 February.
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