Bristol City boss Gary Johnson has further strengthened his squad with the signing of goalkeeper Dean Gerken and defender Andre Blackman.

Gerken has joined City for an undisclosed fee and the 24-year-old will provide competition for Adriano Basso and Stephen Henderson, who is ruled out for six weeks with a broken metatarsal.

Blackman, 18, was released by Portsmouth at the end of last season, having been a regular in the Premier League club's reserve team.

Bristol City manager Johnson has now recruited three players this week, following the signing of striker David Clarkson from Motherwell on Monday.

Gerken, who played 119 times for Colchester, has joined City on a two-year deal.

The 6ft 4ins goalkeeper said: "It's been a whirlwind move for me really, taking just three or four days.

"I'm over the moon with the move. It's a massive club that plays good football. The players always look like they enjoy their football here.

"I know Adriano's a quality keeper. I'm looking forward to working with him and locking horns with him (for the number one spot). I'll put up a strong fight.

"I want to play at the highest level possible. I had two good seasons at Championship level with Colchester before and now I want to play in the Championship again."

He added: "I'm thankful for everything Colchester have done for me but it's the right time to move on.

"A new manager came in with a different view and a different way in which to take the football club.

"I thank the Colchester supporters for their backing during my time there and the club. It's time to move on; that's what happens – it's football."

Johnson believes the signing of Blackman is a further indication that Bristol City are laying exciting foundations for the future.

Blackman had become frustrated at his failure to make inroads into the first-team picture at Portsmouth, and failed to earn a new deal after suffering an ankle injury that required surgery towards the end of the season.

Johnson, however, insists the left-back is not a 'million miles away' from providing Jamie McAllister with competition for his place and believes he joins a group of 'nine or ten' exciting youngsters currently developing at Ashton Gate.

Johnson said: "It is always important to make sure that we have a very good under 21 group as the club becomes bigger. The young players save you a bit of money later on and you don't have to keep paying out millions.

"If you can create your own players that are eventually good enough to play regularly for the first team then they become a big asset to the club.

"I am pleased with our young group as we have nine or ten of very good potential. We are working on improving them every day and they are a very exciting bunch.

"I think Andre has a super future in the game and I don't feel he is a million miles away right now. I think he had become a little frustrated and impatient that he wasn't as close to the Portsmouth first-team as he would have liked.

"He is a confident lad with excellent athleticism and bags of pace so I have got high hopes for him. People at his other clubs have been talking about his potential and this move gives him a chance to show some of it."

Blackman will not be a part of full training when City return for their first day of pre-season this morning. He is continuing his rehabilitation from ankle surgery but Johnson insisted: "He has a problem with his ankle but a specialist has had a look at it and told us it will be fine.

"He has to wait a little while and probably won't have the chance of a reserve team game until the middle of August."

Blackman has yet to feature in a senior first-team game but is aiming to be pushing for a place in the City side as soon as possible after agreeing terms on a two-year deal.

"It is a great opportunity for me," he said. "I want to express myself and show that I am ready for first-team football.

"I'm working every day with the medical team and the aim is to be fit near the end of July. I can't wait to get out there and play, I just have to get over my injury first."

City are set to offer former Chelsea star David Lee a full-time position as an academy coach after a short spell at the end of last season.

Meanwhile, striker Dele Adebola will be unveiled as a Nottingham Forest player later today after agreeing a two-year deal to make the switch from Ashton Gate.