Nicky Robinson’s comeback at the Cardiff Blues has been put into sharper focus after they revealed Gareth Anscombe has been ruled out for six weeks.

Wales fly-half Anscombe is to have surgery on a groin injury, meaning Robinson will come straight onto the bench for Saturday’s home Guinness Pro12 match against Ulster.

Steve Shingler will start at No.10 with Robinson – who has been persuaded to come out of retirement at the age of 34 – among the replacements.

The Blues announced Robinson’s four-month deal earlier this week after young outside-half Jarrod Evans was sidelined with a broken jaw.

But now it has emerged that Anscombe is also facing a lengthy lay-off following his unconvincing display for Wales against Japan.

Robinson, who had hung up his boots in the summer after a spell playing in France, will now deputise for Shingler on Saturday and is currently one of just two fit regular fly-halves at the region.

Sam Warburton returns to the Blues starting line-up after missing the final match of the autumn international series against South Africa with a shoulder injury.

Wales prop Gethin Jenkins also returns and the duo are two of five changes to the side that slipped to defeat to Connacht in Galway last weekend.

Blaine Scully switches to full-back in the absence of Dan Fish with Alex Cuthbert coming into the starting line-up. Lloyd Williams also returns from international duty.

The Blues opened their Pro12 campaign with four victories but have won just once in their last five matches.

Blues coach Danny Wilson said: “We beat Ulster at home last season in quite an exciting game and I envisage something similar on Saturday evening.

“They would have wanted that game last week and are coming into this after three weeks off but they have a star-studded team and their internationals back. They have some real quality.

“We’re disappointed we didn’t pick up anything in Connacht. We certainly created enough opportunities and dropped the ball twice over the line, which could have won the game.

“But one thing we improved was our defence. We’ve spent a lot of time on it in the last couple of weeks and we defended extremely well.

“If we can see that at home and add to our attacking game on our surface it should be an exciting game.”

Blues: B Scully; A Cuthbert, R Lee-Lo, W Halaholo, T James; S Shingler, L Williams; G Jenkins (capt), K Dacey, T Filise, G Earle, J Turnbull, E Jenkins, J Navide, S Warburton.

Reps: M Rees, R Gill, S Andrews, J Hoeata, M Cook, T Williams, N Robinson, M Morgan.

Ulster: C Piutau; T Bowe, L Marshall, S McCloskey, C Gilroy; B Herron, R Pienaar; K McCall, R Herring (capt), W Herbst, P Browne, F van der Merwe, I Henderson, S Reidy, C Henry.

Reps: J Andrew, A Warwick, R Ah You, K Treadwell, C Ross, P Marshall, L Ludik, D Cave.